题目

After a thorough investigation, the policeman declared that the blow on the victim’s head _____ from behind.A. shouldhave been made B. must havebeen made  C. would havebeen made D. ought tohave been made 答案：B把371×28-4÷2的运算顺序改变成先求差，再求商，最后求积，则原式变为：______．