In a shelf, there are $3$ mathematics and $2$ physics books. $A$ student takes a book randomly. If he takes a book randomly, successively for $3$ times by replacing the book already taken every time, then the mean of the number of mathematics books, which is treated as a random variable, is:

  • A
    $\frac{3}{2}$
  • B
    $\frac{129}{125}$
  • C
    $\frac{9}{5}$
  • D
    $\frac{174}{125}$

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