It is not the first time one of Google's famed self-driving cars has been involved in a crash, but it may be the first time it has caused one.
这不是谷歌著名的自动驾驶汽车第一次卷入事故,但这可能是它第一次造成事故。
这是 "It is the first time (that) + 现在完成时" 句型的否定形式。该句型有严格的时态配套规则:主句用 "is" 时,从句必须用现在完成时(have/has done);主句用 "was" 时,从句必须用过去完成时(had done)。
本句主句为 "It is not the first time",从句 "one of Google's famed self-driving cars has been involved in a crash" 使用了现在完成时 "has been involved",完全符合该句型的时态配套要求。
识别要点:1) 主句必须是 "It is/was the first/second/third... time" 结构;2) 从句谓语必须用完成时态;3) that 可以省略(本句即省略)。
常见错误:学习者容易在从句中误用一般过去时,如错误地说 "It is the first time he went there",正确应为 "It is the first time he has gone there"。
可迁移方法:记住口诀 "is 配 have/has done,was 配 had done",并注意该句型表达 "到现在/当时为止第几次做某事" 的含义,强调经历的累积。