keep... from...　prevent... from...　stop... from...
　　keep... from doing... 意思是阻止、防止做某事,它与prevent... from doing...和stop... from doing...同义。其中,prevent... from doing...和stop... from doing...中的介词from可以省略（stop 和 prevent用于被动语态时,其后的from 不能省略）,但keepfrom doing...中的from不能省略。如果省略了from, 那么keep... doing...的意思就成为使一直做。