但stop和prevent后面的from可省略
为什么keep后面的from不可省？？？？？？
因为 stop sb. (from) doing sth 和 prevent sb (from) doing sth 省掉了from 不会影响语义，而 keep sb. from doing sth 省掉from后，意思正好相反：
I kept him working on his homework —— 我一直让他做作业
I kept him from working on his homework —— 我不让他做作业
I kept him working on his homework —— 我一直让他做作业
I kept him from working on his homework —— 我不让他做作业
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第1个回答 2013-02-13
keep后面from省略后就变成另外一个意思，只有在keep from doing sth 时才有阻止做某事的意思，而keep doing sth 就是一直做某事的意思，所以keep后面from不可省略。
第2个回答 2013-02-13
因为如果keep sb from doing sth......省掉之后变成keep sb doing sth意思变为“使某人一直做某事”。所以不能省
第3个回答 2013-02-13
keep doing 表示一直在做，加了from 才能表示prevent的意思
