天线的极化方式有（）、（）、（）极化。
参考答案：水平；垂直；±45
Please do not call me at 8 p.m. because I _______to Beijing. [ ]
A. am going to fly
B. will be flying
C. will fly
D. am to fly
选择填空。
The question is not ______, but I can answer it. [ ]
A. easy
B. hard
C. right
D. okay
