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?（）
A.Steel brush B.Fine emery cloth or steel wool C.A section of the removed compression ring D.A case hardened scraper
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 （）
单项选择题 If a main propulsion diesel engine hunts excessively at idle speed, you should （）
