Consider the following statements $S$ and $R$:
$S: \sin x$ and $\cos x$ are both decreasing functions in the interval $\left( \frac{\pi}{2}, \pi \right)$.
$R:$ If a function $f$ is decreasing in an interval $(a, b)$,then its derivative $f'(x)$ is also decreasing in the interval $(a, b)$.
Which of the following is true?

  • A
    $S$ and $R$ are both false.
  • B
    $S$ and $R$ are both true but $R$ is not the correct explanation for $S$.
  • C
    $S$ is true and $R$ is the correct explanation for $S$.
  • D
    $S$ is true and $R$ is false.

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