One of the main reasons for the increase in greenhouse gases is

Cars and factories emit greenhouse gasses 

C) all of the above hope this

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)