Q31:

When a ton of wheat was being moved from Buffalo to New York City before the opening of the Erie Canal in 1825, it took three weeks and cost $100, but when the canal was used, it took less than eight days and cost less than $6.

1. When a ton of wheat was being moved from Buffalo to New York City before the opening of the Erie Canal in 1825, it took three weeks and cost $100, but when the canal was used, it
2. Moving a ton of wheat from Buffalo to New York City before the opening of the Erie Canal in 1825, it took three weeks and cost $100; using the canal, it
3. Before the opening of the Erie Canal in 1825, moving a ton of wheat from Buffalo to New York City took three weeks and cost $100; on the canal the move
4. In 1825, before opening the Erie Canal, to move a ton of wheat took three weeks from Buffalo to New York City, which cost $100; moving it on the canal
5. To move a ton of wheat in 1825 from Buffalo to New York City took three weeks before the opening of the Erie Canal, costing $100, but in using the canal, the move

答案是C，可是我觉得选A

A里面when..., it...,but when...it....看起来很好的，C 就不平行了

请NN帮助解释一下吧，谢谢！

A is wrong. what is "it"?? "it" in A could be either "the openning" or "a ton of wheat".

哦，有道理。

今天做了很多大全的题，发现很多地方只要it出现就有点指代不明。

呵呵，谢谢解释！