It is very important to slowly open oil drain valves and plugs in the crankcase for which of the following reasons?
a. The oil is very hot
b. Oil can never be drained below the critical minimum level
c. Residual pressure in the crankcase may blow refrigerant vapour and oil out
d. Old oil is contaminated with refrigerant and may be very acidic
e. The oil is very cold, and may cause freeze-burns
Answer: C