题目

.It is the first time the students ________ to Hyde Park.    A. have gone             B. have been gone    C. had gone              D. had been gone 答案：A下列运算正确的是（   ）A. ﹣5（a﹣1）=﹣5a+1 B. a2+a2=a4 C. 3a3•2a2=6a6 D. （﹣a2）3=﹣a6 D 【解析】因为﹣5（a﹣1）=﹣5a+5,所以A错误,因为 a2+a2=2a2,所以B错误,因为3a3•2a2=6a5,所以C错误,因为（﹣a2）3=﹣a6 ,所以D正确,故选D.