题目

A. complete B. pretend C. in turn D. expect E. in returnHowever, the first beggar thought, “I don't want to share. I'll just 【1】 to throw my meat into the pot. They'll never know and I'll eat my meat later.” But he didn't 【2】 that the other beggars all had the same idea and the hut was so dark that no one could see what the others were doing. Finally, one of them suggested that the dish should be ready and, 【3】, each of them helped himself to a bowl. They drank the hot water in 【4】 silence, learning that selfishness doesn't taste all that good.定义在R上的函数f（x）满足：对任意x、y∈R都有f（x）+f（y）=f（ x+y）．（1）求证：函数f（x）是奇函数；（2）如果当x∈（-∞，0）时，有f（x）＞0，求证：f（x）在（-1，1）上是单调递减函数；（3）在满足条件（2）求不等式f（1-2a）+f（4-a2）＞0的a的集合．