题目选项分析

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, thus making it easier for the ant to spread.

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, thereby, it was made easier for the ant to spread.