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题库 / Prep2012-SC-35
The possible long-term health risks to airline personnel who repeatedly cross multiple time zones has been a concern since the first jet transports went into service in the 1950s.
who repeatedly cross multiple time zones has been a concern since the first jet transports went
who are repeatedly crossing multiple time zones has been a concern since the first jet transports that went
who repeatedly cross multiple time zones have been a concern since the first jet transports went
repeatedly crossing multiple time zones has been a concern since the first jet transports went
repeatedly crossing multiple time zones have been a concern since the first jet transports going
题目分析：
since是连词，身后应该连接一个从句，而(B)(E)中since身后均不是完整句，可以排除。在(A)(D)中，主句主语The possible long-term health risks和谓语动词has been主谓不一致，可以排除(A)(D)，答案为(C)。
选项分析：
略
ABD、主谓一致错；主语是risks复数+谓语动词应该为复数
C、since the first jet transports went into service，OK
E、since the first jet transports [going into service，going…定语修饰transports，缺少谓语动词，句子不完整
E选项，担心的对象不能是一个物体。
since可以做连词，也可以做介词。
另外，repeatedly crossing是不是也有问题呢？crossing无时间终结点。
我感觉没问题。。都是先行词省略了
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since是不是也可以作介词，例如since 2017...。那么c和e的差异是否也体现在cross上，譬如c的一般时表示穿越时区是个常态？
可以是介词。但是如果这里是介词的话，那么意思变成了：自从新的飞行器，身体健康就是问题。这显然不合逻辑，肯定是要自从飞行器怎么了，然后身体健康才是问题。
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