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文章开篇通过 'A drug is a chemical substance' 这个 straightforward definition 直接定义了 drug 的本质，紧接着用 'It can bring about a physical, emotional or mental change' 来 elaborate 其作用机制。这种 clear-cut definition 为整篇文章奠定了 conceptual foundation，让读者从一开始就能 grasp 核心概念，避免了对 drugs 这个 term 的误解。通过明确 alcohol、tobacco、caffeine 都属于 drugs，作者 expand 了读者对 drug 这个 concept 的认知范围，这对理解后文的 drug abuse 至关重要。
信号词
is means refers to is defined as can be described as is called represents denotes
仿写： 当你需要 introduce 一个 key concept 时，不妨采用这种 straightforward approach。首先用一个 simple sentence 给出 core definition，比如 'X is Y'，然后立即 follow up 一个补充句来说明其 functions 或 characteristics。关键是要 balance precision and accessibility——定义要 accurate，但也要让 target audience 能够 understand。仿写模版：'[Topic] is [category/nature]. It [key function/characteristic]. [Common examples] are [topic].'
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作者在定义 drug 之后，immediately 提供了 concrete examples：'Alcohol and tobacco are drugs. Caffeine, a substance found in coffee and some soft drinks, is also a drug.' 这些 everyday examples 让抽象的 chemical substance 概念变得 relatable and tangible。通过列举 alcohol、tobacco、caffeine 这些 familiar substances，作者成功 bridge 了 theoretical definition 和 real-life experience 之间的 gap。这种 exemplification 不仅 reinforce 了定义，还 challenge 了读者可能存在的 misconception——很多人不会把 caffeine 视为 drug。
信号词
for example for instance such as like including namely as take...for example
仿写： 在给出一个 general statement 或 definition 后，立即 provide 2-3 个 specific examples。选择的 examples 要符合 target audience 的 life experience，最好是 commonly known 的事物。可以用 simple listing 的方式，也可以加入 brief description 来增强 clarity。仿写模版：'[General concept]. [Example 1] and [Example 2] are [concept]. [Example 3], [brief description], is also [concept].'
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在 第2段 开头，作者给出了 drug abuse 的 precise definition：'Drug abuse is the use of a drug legal or illegal that hurts a person or someone close to him.' 这个 definition 非常 strategic，因为它不仅定义了 abuse 的 nature（harmful use），还 clarify 了一个重要 point——even legal drugs 可以被 abuse。紧接着，'A drug user is the person who takes the drug' 这个 simple definition 为后面的 classification 做了 transition。这两个 definitions 共同构建了文章第二段的 conceptual framework。
信号词
is means refers to is defined as can be described as represents
仿写： 当引入 new terms 或 concepts 时，用清晰的 definition sentence 来 anchor 你的 explanation。Structure 可以是：'[Term] is [what it does/is] that [key characteristic].' 注意在 definition 中 incorporate 能够 distinguish 该概念与相似概念的 critical feature。如果有必要，可以 follow up 一个 contrasting definition 来 clarify boundaries。仿写模版：'[Term A] is [action/state] that [harmful/beneficial effect]. [Term B] is [who/what performs the action].'
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第2段 的核心是对 drug users 进行 systematic classification：experimental users、recreational users、regular users、dependent users。这种 categorization 不是 random 的，而是按照 usage frequency 和 dependency level 呈现出 progressive pattern。每个 category 都配有 clear description：experimental users 'may try drugs once or twice'，recreational users 'take drugs to get high'，regular users 'take drugs all the time' but maintain routine，dependent users 'can't relate to anything but drugs'。这种 hierarchical classification 帮助读者理解 drug use 从 casual experimentation 到 severe addiction 的 spectrum，为第三段关于 dependency 和 being 'hooked' 的讨论 pave the way。
信号词
kinds of types of categories of classes of divided into classified as can be grouped into fall into include
仿写： 当你需要 explain 一个 complex phenomenon 时，考虑是否可以将其 break down into categories。首先 identify 一个 logical criterion（比如 frequency、intensity、purpose），然后 establish 3-5 个 distinct types。对每个 type，provide a concise label 和 defining characteristics。可以用 parallel structure 来 present each category，这样能增强 readability。最好按照某种 logical order 排列 categories，比如从 mild to severe，从 common to rare。仿写模版：'There are [number] kinds/types of [subject]. [Type 1] [verb/action]. They [characteristic]. [Type 2] [verb/action]. They [characteristic]...'
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在 classify 每种 drug user 后，作者不止于 label，而是对每个 type 进行 detailed interpretation。比如 experimental users 后面 explain 'They want to see what the effects will be'，recreational users 后 elaborate 'They use drugs with friends or at parties to get into the mood'。这些 interpretative statements 揭示了 underlying motivations 和 behavioral patterns，让 classification 不仅是 superficial labels，而是 meaningful distinctions。特别是对 dependent users 的诠释 'They feel extreme mental or physical pain without drugs' 揭示了 addiction 的 physiological and psychological dimensions，为第三段关于 dependency 的讨论做了 smooth transition。
信号词
that is in other words this means namely to put it another way which means what this means is
仿写： 在 present 一个 statement 或 category 后，不要 stop there，而要 add a follow-up sentence 来 interpret or explain。可以 reveal motivations（'They want to...'），describe behaviors（'They use... to...'），或 explain consequences。Use connecting words 虽然不总是必要，但能让 interpretation 和 main statement 的 relationship 更清晰。仿写模版：'[Statement/Category]. They [action] [purpose/result]. Their [characteristic] [explanation of why/how].'
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在 第3段，作者 define 了 drug dependency 的状态：'They are dependent upon drugs' 和 'they can't do without them'。虽然不是 traditional 'X is Y' 的 definition format，但这两个 statements 共同构成了对 dependence 这个 state 的 operational definition。更重要的是，后面通过 'the person is hooked' 这个 colloquial term 来 restate dependency，这种 informal definition 让 abstract concept 变得更 relatable。这个 definition 是文章的 climax，因为它 synthesize 了前面关于 drug users 的 classification，指出了 progression 的 end point。
信号词
are is become are called are known as turn into
仿写： 除了 traditional 'X is Y' definition，你可以用 behavioral descriptions 或 state descriptions 来 define concepts。Structure 可以是：'They are [state]. They can't [action without something].' 然后可以用一个 familiar term 或 metaphor 来 reinforce：'By this time... the person is [colloquial term].' 这种 combination of formal and informal definitions 能 reach different types of learners。仿写模版：'[People/Things] are [state/condition]. They can't [action] without [object]. The [subject] is [colloquial term].'
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虽然不是 explicit comparison，但 第2段 通过 juxtapose 不同 types of users，implicitly 进行了 comparison。从 experimental（'once or twice'）到 recreational（'get high'）到 regular（'all the time' but 'keep up with normal routine'）再到 dependent（'can't relate to anything but drugs'），每个 category 之间存在 subtle contrast。特别是 regular users 和 dependent users 的对比最为 striking：前者 'able to keep up with normal routine'，后者 'whole life centers around drugs'。这种 implicit comparison 帮助读者 understand the gradual escalation from casual use to addiction。
信号词
but however while whereas unlike in contrast compared to more than less than different from
仿写： 当 present multiple categories 或 stages 时，structure your descriptions 以便 facilitate comparison。Use parallel sentence structures 让 differences stand out。你可以在每个 description 中 include a key differentiating feature，比如 frequency、ability、或 consequence。不需要 explicitly say 'compared to'，通过 careful juxtaposition 就能 achieve comparison effect。仿写模版：'[Type A] [action] [frequency/manner]. They [ability]. [Type B] [action] [different frequency/manner]. They [different ability].'
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第3段 的开头 'It's not always easy to tell if someone is using drugs. In the early stages, drug use is often hard to see' 是对 drug detection difficulty 的 interpretation。作者不是 simply state 一个 fact，而是 explain why dependency 是 dangerous——因为它 develops gradually and invisibly。后面的 interpretation 'Only a few kinds of drugs can cause physical dependence. But almost any drug, when it's misused, can make a person think he needs it all the time' 揭示了 psychological dependency 和 physical dependency 的 distinction，这是 crucial insight。最后 'By this time it's too late' 诠释了 'hooked' state 的 irreversibility，给整篇文章带来 sense of urgency。
信号词
this means in other words the significance is what this suggests the implication is this indicates
仿写： 在 present factual information 后，add interpretative statements 来 explain significance。可以用 'this means'、'the problem is'、'what this suggests is' 等 phrases，但也可以 directly state the interpretation。Focus on revealing 'why this matters'、'what the consequences are'、或 'how this works'。特别是在文章 conclusion，interpretation 能 elevate your writing from informative to insightful。仿写模版：'It's not always [easy/obvious] to [action]. In the [early/initial] stages, [phenomenon] is often [hard to detect]. [Statement]. But [contrasting insight] can [consequence]. By this time [result].'
