People in Brazil celebrate their New Year by the way of splashing water on each other.

While a car passing the wading channel, the car testers carry out wading analysis of the testing car by watching the situation of the firewall being washed by water flow and sealing of the doors and windows by water splashing．

Which of the following is TRUE?____. A: If there is oxygen and fuel in an enclosed tank, there must be an explosion. B: Crankcase explosion is least likely to occur, because there is no air in crankcase. C: The droplets of lubricating oil splashing around in the crankcase is usually too large to start burning. D: The oil/air concentration in crankcase is usually too rich.