Let $f:[-1,1] \rightarrow \mathbf{R}$ be a continuous function. Consider the region
$S=\{(x, y):-1 \leq x \leq 1 \text { and } 0 \leq y \leq f(x)\}$
For which one of the following functions $f$, the area of the region $S$ is the largest?

• A

  $f(x)=\pi^x|\sin \pi x|$.
• B

  $f(x)=\pi^x|\cos \pi x|$.
• Correct answer
  C

  $f(x)=\pi^x\left(1+\left|\tan \frac{\pi x}{10}\right|\right)$.
• D

  $f(x)=\frac{\pi^x}{|x|+1}$.

Hence, the correct answer is option: 'C'.