GWD5-Q34

Many entomologists asy that campaigns to eradicate the fire and 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

请为问这里第一个it指代什么，B为什么错。还有最后的spread在句意上时怎么理解的？谢谢！！

第一个it指代后面的不定式to spread，B当中出现了两个it，按照语法规则，同一句中的同一代词不能指代不同事物，B犯了这个错误，第一个it和第二个it肯定不是同一事物。

spread可以认为是蔓延，展开等意思