$A$ girl holds a book of mass $m$ against a vertical wall with a horizontal force $F$ using her finger,so that the book does not move. The frictional force on the book by the wall is

  • A
    $F$ and along the finger but pointing towards the girl
  • B
    $mg$ and upwards
  • C
    $\mu F$ upwards,where $\mu$ is the coefficient of static friction
  • D
    equal and opposite to the resultant of $F$ and $mg$

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