RL电路过渡过程的时间常数τ＝（）。
A、LR
B、R/L
C、L/R
D、1/（RL）
参考答案：C
Lily gets up ____ 7 o’clock.
A．in
B．on
C．at
D．to
The old man enjoys collecting signatures of famous people _______ famous paintings. [ ]
A. with preference of
B. in preference to
C. in preference for
D. with preference to
