---Tom hurt his left leg in the game this morning.

---Really? It would take at least two weeks ______ he could recover and return to school.

A．when

B．that

C．since

D．before

机车上用来自动或非自动开闭有电流电路的电器称为（）。

A、控制电器

B、保护电器

C、调节电器

D、开关电器