The water-soluble vitamins demonstrated to be toxic in large doses are:

a. vitamins a, d, e, k
b. vitamin c, niacin, vitamin b6 (pyridoxine)
c. calcium, manganese, vitamin b12 (cobalamins)
d. none of the above; water soluble vitamins never cause toxicity

Vitamins are classified as either fat soluble (vitamins A, D, E and K) or water soluble (vitamins B and C). This difference between the two groups is very important. It determines how each vitamin acts within the body. Fat soluble vitamins, once they have been stored in tissues in the body, tend to remain there. This means that if a person takes in too much of a fat soluble vitamin, over time they can have too much of that vitamin present in their body, a potentially dangerous condition called hypervitaminosis (literally, too much vitamin in the body). Water-soluble vitamins, including vitamins C and B, are excreted much more quickly than fat-soluble vitamins, and they need to be replaced more frequently.

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)