单项选择题
Using a file without a handle may result in （）
A.your work becoming rounded B.injury to your hand C.overheating of the file D.pinning
单项选择题 Before welding is permitted on a fuel tank, it must be certified or declared （）
单项选择题 Safe welding practice requires （）
单项选择题 Which lubricating oil additive is used in diesel engines to reduce the tendency for sludge and varnish to form on the engine parts?（）
