Which one of the following statements is true?

$A$ point object is kept in front of a plane mirror. The plane mirror is performing $SHM$ with an amplitude of $2 \ cm$. The plane mirror moves along the $x$-axis,and the $x$-axis is normal to the mirror. The amplitude of the mirror is such that the object is always in front of the mirror. The amplitude of the $SHM$ of the image is ....... $cm$.

The focal length of a plane mirror is:

Two mirrors are inclined at an angle $\theta$ as shown in the figure. $A$ light ray is incident parallel to one of the mirrors. The ray will start retracing its path after the third reflection if $\theta = ........$

$A$ beam of light from a source $L$ is incident normally on a plane mirror fixed at a certain distance $x$ from the source. The beam is reflected back as a spot on a scale placed just above the source $L$. When the mirror is rotated through a small angle $\theta$,the spot of the light is found to move through a distance $y$ on the scale. The angle $\theta$ is given by

Two plane mirrors are placed at an angle of $60^\circ$. $A$ horizontal light ray is reflected by the first mirror and then by the second mirror. The total deviation will be ........... $^\circ$.