某机械的机械效率是85%，它的意义是（ ）
A：总功中有85%用来克服额外阻力做功
B：总功中有15%用来克服额外阻力做功
C：总功中有15%用来克服有用阻力做功
D：它只做了85%的功
Miss Brown, we cleaning our classroom. Can we go home now?
She didn't wear it.____
