【单选题】Although lube oils used in the main lubricating service systems should have a relatively high flash point to avoid ignition, they can create smoke and fire hazards when they()
A.
are exposed to a vacuum
B.
come in contact with extremely hot surfaces
C.
are reduced in temperature to just above the pour point
【简答题】Solutions: a. increased the on gas and used the money to create a new bus system b. put more lanes around the city c. on Sundays and holidays, the city's main streets are also to cars