单项选择题
A.pumping action of the piston
B.pressure of the fuel charge
C.vacuum developed in the manifold
D.pressure of the fresh air charge
单项选择题 Which of the listed items should be secured before performing any maintenance on a solenoid operated air start valve?（）
单项选择题 A diesel engine experiences a sudden loss in speed, accompanied by black exhaust smoke, with the fuel rack at maximum, and speed remaining below normal the probable（）
单项选择题 Which of the following problems can occur if you continually fail to drain off condensate from a starting air receiver?（）