If the function $P[X = x] = \begin{cases} \frac{K \cdot 2^x}{x!}, & x = 0, 1, 2, 3 \\ 0, & \text{otherwise} \end{cases}$ forms a probability mass function (p.m.f.),then the value of $K$ is:

  • A
    $\frac{5}{19}$
  • B
    $\frac{2}{19}$
  • C
    $\frac{3}{19}$
  • D
    $\frac{1}{19}$

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