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