$5.$Which material property is most critical when selecting a spring wire for high$-$temperature applications?

A$)$ Color stability at high temperatures

B$)$ Electrical conductivity

C$)$ Creep resistance

D$)$ Light emission properties

$6.$Pre$-$stressing a helical spring is done to:

A$)$ Improve its aesthetics

B$)$ Increase its electrical conductivity

C$)$ Remove residual internal stresses

D$)$ Enhance its load$-$bearing capacity