单项选择题
Which of the files listed is tapered on three sides and is used to file acute internal angles?（）
A.Mill B.Round C.Square D.Triangular
单项选择题 Using a file without a handle may result in （）
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 （）
