单项选择题
Which of the fuel injection systems listed uses a spring loaded differential spray needle valve and individual pump for each cylinder?（）
A.Common-rail injection B.Air injection C.Jerk pump injection D.Distribution injection
单项选择题 The mode of control employed by an alarm circuit is a （）
单项选择题 The meat box temperature control circuit, as used in ship service refrigeration system, is an example of （）
单项选择题 The two most common gases used in pneumatic system are （）
