An electron is moving along the positive $X$-axis. You want to apply a magnetic field for a short time so that the electron may reverse its direction and move parallel to the negative $X$-axis. This can be done by applying the magnetic field along

  • A

    $Y$-axis

  • B

    $X$-axis

  • C

    $Y$-axis only

  • D

    None of these

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