高考语法解析一： see sb. doing sth与 see sb. do sth

see sb. doing sth, 可否与 see sb. do sth.互换?

　　<答>. 不能,虽然某些动词如:see, hear, notice, watch.等后接动词-ing 形式或不定式(不带to)作宾语补足语都可以.但意思上有区别.比较:

　　I saw them playing basketball at 5 p.m. yesterday.(打篮球的动作正在进行,表示部分进行着的动作.)
　　I saw them play basketball yesterday. (打篮球的动作已完成,表示全过程的动作.)

　　练习: 用所给的适当形式填空.
　　1). We watched them ________ (get) off the bus,__________ (cross) the street and _________ (disappear) among the people.
　　2). Suddenly we heard someone __________ (cry) for help.

　　be about to do 是什么意思?

　　<答>.be about to (do sth.) 表示将来,意为"马上就要"或"正要"例如:
　　She is about to leave. 她马上就要动身了.

　　注释:
　　1). 本结构后通常不能有 immediately, tomorrow, next week 等时间状语.如"我立刻就走"不可说成 I am about to go immediately. (应把immediately 删去)
　　2). be about to do sth. 可与be about doing sth. 换用
　　3). be about 之间加just 是美国口语用法.

　　练习:选择答案填空.
　　He is about ________.
　　A. to start this afternoon B. to start C. to starting D. to be starting


　　答案: get, cross, disappear. crying. B