Solve the Problem $G = P ( x , y ) i + Q ( x , y ) j$

Solve the problem.
-Find a field $G = P ( x , y ) i + Q ( x , y ) j$ in the $x y$ -plane with the property that at any point $( a , b ) z ( 0,0 ) , G$ is a vector of magnitude $\sqrt { \mathrm { a } ^ { 2 } + \mathrm { b } ^ { 2 } }$ tangent to the circle $\mathrm { x } ^ { 2 } + \mathrm { y } ^ { 2 } = \mathrm { a } ^ { 2 } + \mathrm { b } ^ { 2 }$ and pointing in the clockwise direction.

A) $x \mathbf { i } + y \mathbf { j }$
B) $y i - x j$
C) $x \mathbf { i } - y \mathbf { j }$
D) $- y \mathbf { i } + x \mathbf { j }$