We must do something to ________ factories ________ waste water into the river before it is cleaned.A.stop; pouringB.prevent; to pourC.keep; pouringD.stop; to pour
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A解析stop/ prevent sb. /sth. (from) doing sth. 阻止某人／物做某事，from可以省略；keep sb. /sth. from doing也是阻止某人／物或某事，但是from不可省略。