求助一道GWD的题哦

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：D

解法：逻辑意思，看懂题干的意思自然明白了！

至于其他选项的错误——指代不清；