He worked hard and achieved what he set out to do, but ________ what he had owned, including his health and his marriage.

A．at the mercy of

B．at the risk of

C．at the cost of

D．at the service of

如果想从字符串“计算机等级考试”中取出“考试”，这两个字，下列函数使用正确的是( )。

A) SUBSTR("计算机等级考试",11)
B) SUBSTR("计算机等级考试",5,3)
C) RIGHT("计算机等级考试",2)
D) LEFT("计算机等级考试",4)