The points of extrema of $f(x) = \int_0^x \frac{\sin t}{t} dt$ in the domain $x > 0$ are

• A
  $(2n + 1)\frac{\pi}{2}; n = 1, 2, \dots$
• B
  $(4n + 1)\frac{\pi}{2}; n = 1, 2, \dots$
• C
  $(2n + 1)\frac{\pi}{4}; n = 1, 2, \dots$
• D
  $n\pi; n = 1, 2, \dots$