第一节 单项填空

从A、B、C、D四个选项中，选出可以填入空白处的最佳选项。

At 13 he was sent to a shop, ______ he learned the business.

A．your computer will always keep safe the important information
B．computer problems are easy to deal with
C．you will have to replace your computer system sooner or later
D．you must change your system regularly