网络仿真中需要的天线数据文件具体包括（）。
A.广播波束
B.业务波束的水平
C.垂直方向图
D.增益
参考答案：A, B, C, D
Mr Smith ______ a book about China last year but I don’t know whether he has finished it.
A．has written
B．wrote
C．had written
D．was writing
---Your classroom report is so wonderful.
---I wrote for 3 hours ___________ I finished it.
A．when
B．if
C．before
D．after
