可编程序控制器在输入端使用了（），来提高系统的抗干扰能力。
A、晶闸管
B、继电器
C、晶体管
D、光电耦合器
参考答案：D
Byron Campbell purchased 300 shares of Crescent, Inc. , stock at a price of $80 per share. The purchase was made on margin with an initial margin requirement of 50 percent. Assuming the maintenance margin is 25 percent, the stock price of Crescent, Inc. has to fall below what level for Campbell to receive a margin call（）
A. $40.00.
B. $30.00.
C. $53.33.
比一比，组词语。
扎( )礼( ) 课( )棵( )
期( )欺( ) 令( )今( )
轮( )论( ) 坏( )环( )
挑( )跳( ) 辛( )幸( )
