查看原题
设 $f\left(x y, \frac{x}{y}\right)=(x+y)^2$, 则 $f(x, y)= $.
A. $x^2\left(y+\frac{1}{y}\right)^2 ;$     B. $\frac{x}{y}(1+y)^2$;     C. $y^2\left(x+\frac{1}{x}\right)^2$;     D. $\frac{y}{x}(1+y)^2$.         
不再提醒