单项选择题
Fuel injection valves should be taken out, cleaned, and lifting checked every （）.
A.two to four months B.four to six months C.six to eight months
单项选择题 Fuel injection uses the jet pump system and a Woodward type hydraulic （） is used to control engine speed.
单项选择题 Fuel injected into a diesel engines cylinder is ignited by （）.
单项选择题 Fuel has been injected but ignition fails The possible cause may be （）.
