多旋翼是否可以任意方向为头？为什么？
参考答案：
可以，设置飞控为无头模式。
Guess what! I came across my primary school science teacher this morning, ______ I have lost touch for almost 20 years.
A．of which
B．when
C．with whom
D．who
I like comedies ______ I don't like thrillers. [ ]
A. and
B. or
C. but
D. so
