Supposed that $x$ and $y$ are nonzero real numbers such that $\frac{3 x+y}{x-3 y}=-2$. What is the value of $\frac{x+3 y}{3 x-y}$? (2017 AMC 10B Problems, Question \#4) 
选项为:A:$$-3$$  B:$$-1$$  C:$$1$$  D:$$2$$  E:$$3$$  请回答其中一个选项.