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.

在对文件进行操作的过程中，若要是文件位置的指针回到文件的开头，应使用的函数是 【20】 。