题目

The moment I got home, I found I ______ my jacket on the playground.   A. had left     B. left       C. have left    D. was leaving 答案：A 已知函数的定义域为,且满足条件:①；②；③当时,.（1）求证:为偶函数；（2）讨论函数的单调性；（3）求不等式的解集.