1.若2x-3y=0,则x+y/x-y(是个分数额)=( )A.-5 B.5 C.±5 D.42.若x-2y/3y-x=2/3,则y：x等于( )A.5/12 B.12/5 C.-5/12 D.-12/53.若4x=7y+5z,2x+y=z,则x：y：z的值为( )A.2:1:(-1) B.2:1:3 C.2:(-1):3 D.3:2:1

由2x-3y=0得：
2x＝3y
x=3y/2
把 x=3y/2代入(x+y)/(x-y)
=(3y/2+y)/(3y/2-y)
=(5/2)/(1/2)
=5
选B
由(x-2y)/(3y-x)=2/3得：
2(3y-x)=3(x-2y)
6y-2x=3x-6y
12y=5x
y:=5:12
选A
4x=7y+5z,2x+y=z得：
4x-7y=5z (1)
2x+y=z (2)
(2)*2-(1)得:
9y=-3z
y=-z/3
把 y=-z/3代入 (2)得：
2x-z/3=z
2x=4z/3
x=2z/3
所以x:y:z
= (2/3):(-z/3):z
=2:(-1):3
选C