It is really meaningful __________ some children who don't have money to go
to school. (A) teaching (B) not to teach (C) that teach (D) to teach
这题的答案是D. 可是我问了很多外国人，都说A也可以。
请问各位有何高见?

我也觉得是D 问外国人的时候没顺便问原因吗？

It is fun playing outside. It is fun to play outside.这两句话有差吗?

楼上，一个是讲经验，一个是估算（大概吧）

这边两个都可以。但ing是代表已经做过了，在说经验to+v 则指假设一般情况(教xxx很有意义)