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
這題的答案是D. 可是我問了很多外國人，都說A也可以。
請問各位有何高見?

我也覺得是D 問外國人的時候沒順便問原因嗎？

It is fun playing outside. It is fun to play outside.這兩句話有差嗎?

樓上，一個是講經驗，一個是估算（大概吧）

這邊兩個都可以。但ing是代表已經做過了，在說經驗to+v 則指假設一般情況(教xxx很有意義)