题目

设f(x)为定义在R上的奇函数，当x≥0时，f(x)=+2x+m (m为常数)，则（ ） A．3                 B．1              C．              D． 答案：DThese students are quick at learning. We’ll have them __________ with new methods.A．trainingB．to trainC．to be trainedD．trained