Which of the following best describes sports protective equipment?
a. protective equipment is a key part of safe sports.

equipment should be used during games, but not practice.
b.

there's no "right" way to use protective equipment.
c.

you should use only protective equipment that is comfortable.
d.

Protective equipment is a key part of safe sports.

Protective equipment IS a key part of safe sports. Without it, you're exposed to easy injuries. Equipment should be used during games, and also practice. So, B is out of the picture. There is a right way to use protective equipment, so C is also out. The last option is a little in the middle. Yes, you should wear protective equipment that is comfortable, but sometimes that's not exactly the case. 

There are eight major endocrine glands, each with a different function: pituitary gland: the “brain” of the endocrine system; regulates all seven of the other glands and secretes growth hormone.thyroid: regulates a person’s metabolic rate, which is the amount of energy expended daily by a person at rest.thymus: assists in the development of a person’s immune system.adrenal gland: regulates fluid and sodium balance within the body, and secretes epinephrine (“adrenaline”) when the body is under stress, producing the fight-or-flight response.ovaries (in females) and testes (in males): control the development of secondary sex characteristics.pancreatic islets: regulate blood sugar.pineal gland: regulates biorhythms and mood, and stimulates the onset of puberty.

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)