1.感官动词用法之一：see, hear, listen to, watch, notice等词，后接宾语，再接动词原形或ing形式。前者表全过程，后者表正在进行。句中有频率词时，以上的词也常跟动词原形。 I heard someone knocking at the door when I fell asleep.
(我入睡时有人正敲门) I heard someone knock at the door three times.
I often watch my classmates play volleyball after school.(此处有频率词often)
We saw him go into the restaurant.
→ He was seen to go into the restaurant.
I hear the boy cry every day.
→ The boy is heard to cry every day.
2.感官动词用法之二：look, sound, smell, taste, feel可当系动词，后接形容词： He looks angry. It sounds good. The flowers smell beautiful. The sweets taste sweet. The silk feels soft. I felt tired. They all looked tired.
这些动词都不用于被动语态。如：The sweets are tasted sweet.是个病句。 注意：如果加介词like, 则后不可接形容词，而接名词或代词：
He looks like his mother. That sounds like a good idea. It sounds like great fun. It smells like a flower. It tastes like salt.
感官动词 see, watch, observe, notice, look at, hear, listen to, smell, taste, feel + do 表示动作的完整性，真实性；+doing 表示动作的连续性，
I saw him work in the garden yesterday.
I saw him working in the garden yesterday.（强调"我见他正干活"这个动作） 昨天我见他正在花园里干活。
1）They knew her very well. They had seen her ___ up from childhood.
A. grow B. grew C. was growing D. to grow
的动作，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. 本题强调其动作，正在河边玩，应此用see sb. doing sth句型。
begin / start to do sth
begin / start doing sth.
How old were you when you first started playing the piano?
2) begin, start用进行时时，后面动词用不定式to do
I was beginning to get angry。
3) 在attempt, intend, begin, start 后接know, understand, realize这类动词时，常用不定式to do。
I begin to understand the truth。
It began to melt.
mean to do 打算、想
mean doing 意味着
I mean to go, but my father would not allow me to. 我想去，但是我父亲不肯让我去。
To raise wage means increasing purchasing power. 赠加工资意味着增加购买力。