单项选择题
A.moisture emulsification of the bearing grease
B.insufficient circulation and overheating of the bearing
C.proper grease circulation to cool the bearing
D.sliding friction between balls and races
单项选择题 Aqueous Film Forming Foam (AFFF), commonly known as ‘light water’, is especially suitable for fighting （）
单项选择题 Which of the following statements concerning the water tube and fire tube boilers is not true?（）
单项选择题 Which one of following statement is not true concerning the suitable sites of the direct acting relief valve and the pilot operated relieve valve?（）