[求助]gwd10-q20

endless1990

In the mid-1970’s, since birds were overcome by pollution, and routinely falling from the sky above Los Angeles freeways, this prompted officials in California
to devise a plan that reduced automobile emissions.

• since birds were overcome by pollution, and routinely falling from the sky above Los Angeles freeways, this prompted[CH1] officials in California
  to devise a plan that reduced

since birds that had been overcome by pollution were routinely falling from the sky above Los Angeles freeways, it[CH2] prompted officials in California
to devise a plan that would reduce

birds had been overcome[CH3] by pollution and routinely fell from the sky above Los Angeles freeways, prompting officials in California to devise a plan that reduced

birds overcome by pollution routinely fell from the sky above Los Angeles freeways, prompting officials in California to devise a plan to reduce

birds [CH4]overcome by pollution and routinely falling from the sky above Los Angeles freeways were prompting officials in California
to devise a plan to reduce
答案是D,请问C的前半句的时态错在哪里？

windows10

虽然我觉得C和D的前半句都对，甚至说C的时态更合逻辑，但是我还是没有见过一句里面两个并列谓语有两个时态的

xiruihuang

用过去完成时要具备两个条件：
1.有时间标志表示过去的过去
2.表示的是已经完成的动作
C选项中，rutinely fell表示的是发生在过去的一般情况，而这里用and 连接的overcome和fell是具有承接关系的，也就是说，表示这样一种过去的一般情况：first overcome by pollution, then fell。这里用and连接来表达。
如果前半部分用了had overcome，暗示overcome的动作是发生在过去的过去，也就是说在fell这个动作发生的时候可能overcome这个动作是已经完成的，不再有的，这样从逻辑上来说就不对了，因为overcome和fell是发生在同一时间点的具有先后顺序的两个动作。

augest

D 选项 a plan to ....  表示这个plan的目的

C 选项 a plan that ..... 不合逻辑，计划本身不能降低排放