Answer
a) False b) False c) True
Work Step by Step
Need to differentiate each option to check whether the original integral is true or not.
a) $\dfrac{d}{dx}[\dfrac{x^2}{2} \sin x+C]=x \sin x+\dfrac{x^2}{2}\ne x \sin x$; False
b) $\dfrac{d}{dx}[- x \cos x+C]=-\cos x+x \sin x \ne x \sin x$; False
c) $\dfrac{d}{dx}[- x \cos x+\sin x+C]=-\cos x+x \sin x+\cos x = x \sin x$ ; True