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.
which made it easier for them
which makes it easier for it
thus making it easier for them
thus making it easier for the ant
thereby, it was made easier for the ant
it 做形式主语指to spread
make to spread easier for the ant
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