A.12x2=7x+1 B.12x2=7x-1 C.12x2=x+1 D.12x2=x-1 E.12x2=1-x 1The nuclear force is a ……. range force. (20) The ratio of mass to volume is defined as ……… . (21) The density of ice is ……….. than that of water.

A.12x2=7x+1 B.12x2=7x-1 C.12x2=x+1 D.12x2=x-1 E.12x2=1-x The solution set of the system of equation x-y=3, x2-y2=21 is A.{(2,5)} B.{(5,2)} C. {5,2} D.{(2,5),(5,2)} E. None of these 14.The solution set