Which of the Following Is an Exact Differential Equation?
$( y \sin x - 3 \cot y ) d x + ( 3 x \sin y - \cos x ) d y$

Multiple Choice

Which of the following is an exact differential equation?

A) $( y \sin x - 3 \cot y ) d x + ( 3 x \sin y - \cos x ) d y$
B) $( y \sin x - 3 \cos y ) d x + ( 3 x \sin y - \cot x ) d y$
C) $( y \sin x - 3 \cos y ) d x + ( 3 x \sec y - \cos x ) d y$
D) $( y \sin x - 3 \cos y ) d x + ( 3 x \sin y - \cos x ) d y$
E) $( y \sec x - 3 \cos y ) d x + ( 3 x \sin y - \cos x ) d y$