单项选择题
The shape of a cam on a diesel engine determines the valve’s （）
A.point of opening B.speed of opening C.lift from its seat D.all of the above
单项选择题 Which of the listed devices could be used as a ring groove tool during preparation for the installation of new rings?（）
单项选择题 The main source of fuel injection system malfunctions is （）
单项选择题 The most crucial time for any bearing with regards to lubrication is （）
