题目

Children can ________ a lot _________ this new kind of school system. A. benefit; from    B. benefit; with   C. change; from    D. lose; from 答案：A如果a，b都代表有理数，并且a+b=0，则A.a，b都是0B.a，b之一是0C.a，b互为相反数D.a，b互为倒数