Question

Playing computer games is bad for our health,but ___(spend)some time reading is good for us.

Answer 1

为你解答。
Playing computer games is bad for our health,but (spending) some time reading is good for us.
句意：玩电脑游戏对健康有害，但花时间读书对我们有益。
解释：填动名词doing，作为句子的主语。

追问

可我没见过spend加ing呀

追答

有的。而且前一句的句式与后一句完全相同，主语是playing，你自己可以作一下比较。