$12.$ The primary function of the extra leaves in a multi$-$leaf spring is to:

A$)$ Increase the spring's overall stiffness and load capacity

B$)$ Improve the vehicle's acceleration

C$)$ Decorate the underside of the vehicle

D$)$ Decrease manufacturing costs

$14.$ The primary advantage of using helical springs made from non$-$circular wire is:

A$)$ Improved aesthetic appeal

B$)$ Enhanced strength and durability for a given weight

C$)$ Reduced manufacturing time

D$)$ Increased electrical conductivity