Consider the space group No$.15,C\frac{2}{c}.$

$($a$)$ In a unit cell, draw the plan view of the symmetry elements.

$($b$)$ In a separate corresponding unit cell, draw the plan view of the distribution of asymmetric units in their general positions.

$($c$)$ Draw the $3$D perspective view of the unit cell and indicate the positions of the asymmetric units.