Which of the following tests are NOT used to examine the weak form of the efficient market hypothesis Those that examine:（）

A. whether security returns are independent over time.

B. a security’s return relative to the market return.

C. whether excess returns can be obtained from using mechanical trading rules.

对于感性负载的整流电路，要在感性负载两端并联一个（），使晶闸管在电源电压接近零值时能可靠地关断。

A、正向二极管

B、反向二极管

C、三极管

D、滤波电抗器