【一个英语选择题····求助I'lltryandgiveyou_____quickexplanationofhow____machinethatweboughtyesterdayworks.A,a:theB,;theC,the;aD,a;】

　　一个英语选择题····求助I'lltryandgiveyou_____quickexplanationofhow____machinethatweboughtyesterdayworks.

　　A,a:theB,;theC,the;aD,a;