$x$ and $y$ are positive real numbers for which
$$\frac { x - y } { x \sqrt { y } + y \sqrt { x } } = \frac { 1 } { \sqrt { x } }$$
the equality holds.
Accordingly, what is the ratio $\frac { x } { y }$?
A) 4
B) 2
C) 1
D) $\frac { 9 } { 4 }$
E) $\frac { 1 } { 2 }$