为什么用be busy doing而不是be busy to do

为什么是be busy doing而不是be busy to do "be busy to do " 还是 " be busy doing" 忙于做某事为什么要用be busy doing sth 可以用be busy to do sth吗 1.be busy(in )doing 2.be busy to do 3.be busy with 4.be busy be busy to do be busy to do sth.和be busy doing的区别 be busy doing sth 和be busy to do sth 的区别 是be busy doing sth还是be busy to do sth? be afraid of doing sth be busy doing sth be glad to do buy s ask sb to do sth be afraid of doing be busy doing be late fo be busy doing造句 用want to dop,want sb to do ,be busy doing.这三种句式各造一句短语.