风电场做无功功率调节能力的测试时计算风电场输出有功功率和无功功率，其有功功率和无功功率为（）分钟平均值。
A.1
B.2
C.3
D.4
参考答案：A
已知函数f(x)＝mx2－mx－1.
（1）若对于x∈R，f(x)＜0恒成立，求实数m的取值范围；
（2）若对于x∈[1,3]，f(x)＜5－m恒成立，求实数m的取值范围．
—The light in his room is still on. Do you know _______?
—In order to get ready for the coming exam.
A．why he stays up so late
B．if he works hard
C．what he is doing
D．when he will stop working
