Aspraina. is a stretch and/or tear of a ligamentb. is the most painful of all athletic injuries c. is an injury that can never be healedd. can be completely avoided by stretching

A sprain would be A.
A sprain is usually easily healed over time, not scientifically the most painful athletic injury, and is an injury usually caused by some sort of accident.
A sprain is when you stretch or tear a ligament, which is the fibrous tissue connecting bones and joints.

The person who utilize the progression principle will keep adding the difficulty of the exercise that he's doing, while the person who does not, will only stay stagnant.  the person that utilize progression principle, will get a stronger endurance because now his body is conditioned to do harsher routines.{the answer was already on verified)