1) 談及一項(xiàng)長(zhǎng)期活動(dòng)或開始一種習(xí)慣時(shí)，使用doing。

　　How old were you when you first started playing the piano? 你幾歲時(shí)開始彈鋼琴?

　　2) begin, start用進(jìn)行時(shí)時(shí)，后面動(dòng)詞用不定式to do

　　I was beginning to get angry.　我開始生起氣來。

　　3) 在attempt, intend, begin, start 后接know, understand, realize這類動(dòng)詞時(shí)，常用不定式to do。

　　I begin to understand the truth.　我開始明白真相。

　　4) 物作主語時(shí)

　　It began to melt。

　　感官動(dòng)詞 + doing/to do

　　感官動(dòng)詞 see, watch, observe, notice, look at, hear, listen to, smell, taste, feel + do　 表示動(dòng)作的完整性，真實(shí)性;+doing 表示動(dòng)作的連續(xù)性，進(jìn)行性

　　I saw him work in the garden yesterday.　昨天我看見他在花園里干活了。(強(qiáng)調(diào)"我看見了"這個(gè)事實(shí))

　　I saw him working in the garden yesterday. (強(qiáng)調(diào)"我見他正干活"這個(gè)動(dòng)作)昨天我見他正在花園里干活。

　　典型例題

　　1) They knew her very well. They had seen her ___ up from childhood.

　　A. grow　 B. grew　 C. was growing　 D. to grow

　　答案：A. 因題意為，他們看著她長(zhǎng)大，因此強(qiáng)調(diào)的是成長(zhǎng)的過程，而非正在長(zhǎng)的動(dòng)作，因此用see sb do sth。的句型。

　　2) The missing boy was last seen ___ near the river.

　　A. playing　 B. to be playing　　C. play　　D. to play

　　答案：A. 本題強(qiáng)調(diào)其動(dòng)作，正在河邊玩，應(yīng)此用see sb. doing sth句型。