When in operation, it is unavoidable that a small amount of oil _____ through leakage, and

When in operation, it is unavoidable that a small amount of oil _____ through leakage, and in order to compensate for these leaks the system is connected to a feed pump.

A.escapes

B.overheats

C.expands

D.accelerates

请帮忙给出正确答案和分析，谢谢！