单项选择题
A.repack all valve stems
B.lubricate it prior to use
C.replace the foundation bolts
D.balance the warping heads
单项选择题 The color of the flame on a halide torch without any refrigerant present is （）.
单项选择题 The color of the flame on a halide torch without any refrigerant present is （）.
单项选择题 If a refrigeration compressor is running continuously without lowering temperature as normal in the refrigerator, the trouble may be （）.