APU火警探测系统有（）个火警探测器.
A.4
B.3
C.2
D.1
参考答案：C
Though it was raining hard outside, we could see ______ people in the street. [ ]
A. few
B. a few
C. a little
目标控制的基本环节如图1-1所示：
简要叙述目标控制中是如何进行投入的？
