Which of the listed precautions should be
题型：单项选择题
问题：
Which of the listed precautions should be taken when cleaning the internals of a motor with compressed air?（）
A.Open the machine on both ends so as to allow the air and dust to escape
B.Be certain that the circuit breaker is opened and tagged on the feeder panel
C.Be certain that the air is clean and as dry as possible
D.All of the above