The is the lowest level of life's structural hierarchy.

Species are the lowest level of life's structural heierarchy.

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)

My teacher was in one when she was in high school. these abusive lovers can ruin you. mentally and physically. my teacher got a black eye once. she wasn’t able to attend parties or even her moms birthday party all because her bday wanted her to himself.