$5.$ Which factor is NOT typically considered in determining the stiffness of a helical spring?

A$)$ Coil diameter

B$)$ Material type

C$)$ Color of the material

D$)$ Wire diameter

$6.$ The optimum design of a helical spring seeks to minimize:

A$)$ The weight of the spring

B$)$ The cost of production

C$)$ Both A and B

D$)$ Neither A nor B