We have done a lot __the popolation increase.A.to slow down Bstop
问题描述：
We have done a lot __the popolation increase.A.to slow down Bstop
答
to slow down
因为不可能是停止增长，只是减缓增长
答
A
答
选A.介词to在这里表示目的.
we have done a lot to slow down the population increase.
翻译为：为了减少人口增长,我们已经做了很多.