A follower rest should be used with a lathe to machine __________.

Correct Answer: Option C — threads on long slender shafts

A follower rest attaches to the lathe carriage and moves with the cutting tool, providing essential support for long, slender shafts. This prevents the workpiece from springing away from the cutting tool during operations like threading, ensuring dimensional accuracy and preventing the shaft from bending or vibrating under the tool's pressure.