$\text { Find the integrating factor of the differential equation } ( x + 3 y ) d x - 3 \cot x d y = 0 \text { that }$

Multiple Choice

$\text { Find the integrating factor of the differential equation } ( x + 3 y ) d x - 3 \cot x d y = 0 \text { that }$ is a function of x or y alone.

A) $1 + 3 \cot x$
B) $\cos x$
C) $\sin x$
D) $- 3 \cos x$
E) $- 3 \sin x$