In a few years` time,millions of trees those mountains

问题描述:

In a few years` time,millions of trees those mountains
In a few years` time,millions of trees _________(cover) those mountains
为什么不能是have covered

is covering
因为树始终还是覆盖这山
而have covered说明树以前是覆盖的
但现在不再覆盖山了