—How long have you the computer?—For about half a year.A bought B found C had D borrowed

问题补充：

—How long have you the computer?

—For about half a year.

A bought B found C had D borrowed

答案：

解析：考查现在完成时中短暂动词转换为状态性动词。动词buy不能持续很长一段时间，所以，与一段时间连用时，短暂性动词需转换为状态性动词或延续性动词，buy转换为keep“保持，持有，保存”，例如：join转换为be in…或be a member of…。故选C。