$\int_{a}^{x} \frac{sint}{t} dt$ (x > 0), then f(x) has _________________.
(A) a maximum at x = $n\pi$ where n is even
(B) a minimum at x = $n\pi$ where n is odd
(C) a maximum at x = $n\pi$ where n is odd
(D) a minimum at x = $\frac{n\pi}{2}$ where n is odd.