1              GWD-5-Q34:

Many entomologists say that campaigns to eradicate the fire ant in the United States have failed because the chemicals that were used were effective only in wiping out the ant’s natural enemies, which made it easier for them to spread.

A.     which made it easier for them

B.     which makes it easier for it

C.     thus making it easier for them 

D.     thus making it easier for the ant

E.     thereby, it was made easier for the ant

各选项中make后面的it 是形式主语

A、B，which就近指代enemies错

C，them指代不清

D is the best

E，thereby是副词，不能连接两个句子

又是一个分词做结果状语的情况。

我的问题是thus 连接两个句子， 但后面不是一个完整的句子？it做形式主语？我觉得指the chemicals?

 thus making it easier for the ant to spread是状语从句表示结果，THUS在这里是副词而非连词，另外IT是形式主语而非具体指代的词。

另外A是不能指代前面整句话而就近指代其逻辑含义不合理而错误。