Tìm các hàm số \(f\left( x \right)\) biết rằng \(f'\left( x \right) = \dfrac{{{\rm{cos}}\,x}}{{{{\left( {2 + \sin \,x} \right)}^2}}}\).
A.\(f\left( x \right) = \dfrac{{{\rm{sin}}\,x}}{{{{\left( {2 + {\rm{cos}}\,x} \right)}^2}}} + C\).
B.\(f\left( x \right) = - \dfrac{1}{{2 + \sin \,x}} + C\).
C.\(f\left( x \right) = \dfrac{{\sin \,x}}{{2 + \sin \,x}} + C\).
D.\(f\left( x \right) = \dfrac{1}{{2 + {\rm{cos}}\,x}} + C\).