[求助]GWD5-Q34,it指代

feir2004

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GWD5-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

答案是D，虽然作对了，可是不明白D的it指代什么？

jason_alex

好像是指代to spread

cindytim

应该是形式主语吧，不定式做真正的主语

yuyue0277

借宝地问个这道题的相关问题，Thus 在这里和because连用，没有语义重复的错误吗？就好像because。。。。。so一样？
做题的时候上来就派出了BCD，结果发现没有对的

yxas

回ls，because从句是修饰have fail的，我理解这种从句跟副词一样（不对请大家指正）...thus修饰全句