题目

 --- Look! The telephone is broken. Someone damaged it ________ purpose.  ---That may be right. But perhaps it was broken _________ accident.    A. on; by   B. by; by     C. on; on     D. by; on 答案：A若幂函数f（x）=xm2-2m-3（m∈Z）在（O，+∞）上是单调递减的偶函数，则m=11．