be useful to do sth 与be useful in doing sth的区别最好带有例句.

be useful to do sth 与be useful in doing sth的区别最好带有例句. be sure to do sth. be pleased to do sth be able to do sth be going to do sth be let to do sth? be sad to do sth. be made to do sth be obliged to do sth. be used to do sth. be to do sth和will do sth的区别 be worth to do sth 还是be worth doing sth be scared to do sth还是be scared doing sth be surprised at sth.和be surprised to do sth. be glad to do sth 还是be glad doing sth be heard to do sth 还是 be heard doing sth? be used to do sth,be use to doing sth,be use to sth,be use for sth区别 be useful to是加do还是加ing?