题目

You'd better ______ when your mouth is full of food．A.don't speak B.not to speak C.not speak D.not speaking 答案：【答案】C【解析】句意：当你满嘴食物时你最好不要说话。结合句意：当你满嘴食物时你最好不要说话。You'd better not do sth表示“你最好不做某事”，固定句型，排除A、B、D。故选C。在一定质量的溶质质量分数为24%的氯化钾溶液中，加入120g水后，溶液中溶质质量分数降低一半，则原溶液中溶质的质量是（　　）A．14.4gB．28.8gC．120gD．240g