信号设备主要包括哪些？
参考答案：
信号、联锁、闭塞。
在技术经济分析中，一般采用（）计息.
It really puzzles me that sometimes my parents encourage me _____ some friends and discourage me _____
with others. [ ]
A. staying with; to go
B. to stay with; from going
C. staying with; from going
D. to stay with; to go
