$1.$Helical springs designed for compression and extension differ primarily in:

A$)$ The direction in which the load is applied

B$)$ The electrical conductivity of the material used

C$)$ The color variation under load

D$)$ The thermal properties of the material

$2.$The design of a conical spring allows for:

A$)$ A uniform change in color under different lighting conditions

B$)$ The same electrical conductivity as cylindrical springs

C$)$ Variable stiffness and compact storage

D$)$ Improved aesthetic appeal compared to traditional springs