\(\rm\int_0^\pi x\ f(\sin x)\ dx\) is equal to:

• A. \(\rm \pi \int_0^{\pi/2}f (\sin x)\ dx\)
• B. \(\rm \frac{\pi}{2} \int_0^{\pi/2}f (\sin x)\ dx\)
• C. \(\rm \pi \int_0^{\pi/2}f (\cos x)\ dx\)
• D. \(\rm \frac{\pi}{2} \int_0^{\pi}f (\cos x)\ dx\)