（湖南省怀化市2014年高三第二次模拟考试）24. My mother _____ all the cleaning for my family, but recently she has been too busy teaching to do it.

A．will do

B．is doing

C．does

D．had done

关于晨昏线（圈）的叙述，错误的是[ ]

A、是昼夜半球的分界线（圈）

B、晨昏线（圈）上的各地太阳高度均为0

C、晨昏线（圈）在任何时候都等分赤道

D、晨昏线（圈）在任何时候都与经线圈重合