常见的无源电路元件有电阻元件、电感元件和电容元件；常见的有源电路元件是电压源元件和（）。
参考答案：电流源元件
运价是运输产品的销售价格，是（）的货币表现。
A.运输成本
B.运输使用价值
C.运输劳务价值
D.运输使用价值和价值
—She was in class on Friday afternoon, but no one has seen her since.—She ______ an accident.
A. might have B. might have had C. may have D. ought to have had
