doing sth is important为什么是DOING?arriving at the airport early is important.studying english is important为什么是doing arrive at the airport 不行吗

问一个英语语法问题he is doing sth and doing sth还是he is doing sht and is doing sth There is sb. doing sth.是什么意思 there is no point in doing sth. 可以说It is easy doing sth吗 doing sth is 造句 7句 it is difficult doing.sth造句 用it is pleasure doing sth造句 It is worth doing sth同义句 is doing sth 有哪些用法举例说明 用there is sb /sth doing sth,stop sb (from) doing sth造句 there is no sense in doing sth there is no sense in doing sth sb in doing sth 是there is nothing wrong with sb in doing sth it is my frist time to do sth / or doing sth/or do sth? is difficult to do sth .还是to doingis difficult to do sth .还是to doing sth, it is adj.to do sth.it is adj.doing sth.有什么区别it is adj.to do sth.it is adj.doing sth.有什么区别? 求些英语句子组合比如is doing sth ；sb to do sth；enjoy doing sth这样的 our hope is to do sth.还是doing sth.our hope is to do sth.our hope is doing sth.哪个是对的? it is no it is no use doing sth为什么不是it is not use doing sth?