确定地面点位的基本要素是（）、（）和（）。
参考答案：水平角；水平距离；高差
—Where is Tom? I can't find him.
—He ________in the classroom now. [ ]
A. may be
B. maybe
C. willbe
D. was
OFDM符号中的CP可以克服符号间干扰
