题目

 Your cousin is said     a new computer program recently, but do you know when he will finish it? A. to design                                                     B. to be designing          C. to have been designing                                  D. to have designed 答案：C下列各方程是二元一次方程的是A.8x+3y=yB.2xy=3C.2x2-3y=9D.