题目

Mother ________ buy any milk today.A.needs not B.doesn’t need to C.needn’t to D.doesn’t need 答案：【答案】B【解析】句意：妈妈今天不需要买牛奶。考查否定句谓语形式。needs not表述错误；doesn’t need to不必；needn’t to表述错误；doesn’t need不需要。need to do sth.“需要做某事”，作为实义动词变否定句需借助助动词do。故选B。滑轮组之所以有引入额外功是因为考虑到：________和________两个因素．