—_______ John this week?

—Yes.

—Where _______ him?

—In the library.

A．Did you see; did you see

B．Have you seen; did you see

C．Do you see; have you seen

D．Have you seen; have you seen

变压器差动保护投运前做带负荷试验的主要目的是（）。

A、检查电流回路的正确性

B、检查保护定值的正确性

C、检查保护装置的精度

D、检查保护装置的零漂