語法需要,如：
固定結(jié)構(gòu),enjoy doing sth,look forward to doing sth;
時(shí)態(tài)結(jié)構(gòu)：進(jìn)行時(shí)：Look,the boying is playing with his mum.I was cooking when you called yesterday evening.
動(dòng)詞加ing作形容詞：That was really exciting news.He's an interesting man.
動(dòng)詞作主語時(shí),須變成加ing的動(dòng)名詞：Walking is good exercise.Playing a kite is fun.