a$)$ See below as three thin$-$walled beam cross$-$sections of different shapes and of the same area. Each beam is applied with a moment of Mx$.$ Which cross$-$section exhibits the largest deflection? Which cross$-$section exhibits the smallest deflection?

$1.$

$2.$

$3.$

b$)$ A space telescope mirror consists of a rigid substrate $($such as beryllium$)$ and a thin coating of reflective materials $($such as gold$).$ The reflective coating is applied to the substrate by thermal deposition at a high temperature, and then cooled down. Based on your engineering knowledge, discuss about the effect$($s$)$ of this coating process to the mirror structure.