Which procedure involves the use of a radioactive tracer to create an image of the bones

Bone scan? X-ray? This is a logic question, don't get intimidated by the terminology.

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)

A. vitamin c is your answer