If~$\dfrac{y}{x-z}=\dfrac{x+y}{z}=\dfrac{x}{y}$~for three positive numbers x, y and z, all different, then what is the value of~$\dfrac{x}{y}$. 
选项为:A:$$3$$  B:$$5$$  C:$$1$$  D:$$2$$  E:$$6$$  请回答其中一个选项.