$4\mathrm{.}2$ We discussed in class that it is generally a bad idea to use a flat plate $($positioned horizontally$)$ as a

lintel in even relatively short spans. Select the answer that is the most plausible explanation for this.

$($a$)$ Flat plates are difficult to fit into masonry.

$($b$)$ A flat plate of any reasonable width and thickness will not offer an economical solution

because of small moment of inertia per weight ratio.

$($c$)$ Flat plates of required sizes are difficult to find.

$($d$)$ Flat plates have a smaller yield resistance compared with other structural profiles.