Let $f:R \rightarrow R$ be defined as $f(x) = \begin{cases} 0, & x \text{ is irrational} \\ \sin |x|, & x \text{ is rational} \end{cases}$. Then, which of the following is true?

  • A
    $f$ is discontinuous for all $x$
  • B
    $f$ is continuous for all $x$
  • C
    $f$ is discontinuous at $x = k\pi$ where $k$ is an integer
  • D
    $f$ is continuous at $x = k\pi$ where $k$ is an integer

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