单项选择题 The humidifier’s valve of air-conditioner should be （）, when the temperature is 5~8°C in the winter.

单项选择题 In the management of the shafting, because（） carry heavy load and caused high temperature easily, it should be paid attention.

单项选择题 In the shafting management （） should be paid more attention. Ⅰ.f the while metal tailshaft bearing is dripping oil Ⅱ.f some area become blue during the running Ⅲ.he deformation of crankshaft