1. Simplify $\left(\frac{2 x}{x+y}-\frac{4 x}{y-x}\right) \div \frac{8 x}{x^{2}-y^{2}}$, we get ( ).
(A) $\frac{x+3 y}{4}$
(B) $-\frac{x+3 y}{4}$
(C) $-\frac{3 x+y}{4}$
(D) $\frac{3 x+y}{4}$
$\begin{array}{l}\text {-.1.D. } \\ \left(\frac{2 x}{x+y}-\frac{4 x}{y-x}\right) \div \frac{8 x}{x^{2}-y^{2}} \\ =\left(\frac{2 x}{x+y}+\frac{4 x}{x-y}\right) \times \frac{(x+y)(x-y)}{8 x} \\ =\frac{x-y}{4}+\frac{x+y}{2}=\frac{x-y+2 x+2 y}{4}=\frac{3 x+y}{4} .\end{array}$