One of the best ways to avoid injury while biking is to
a. continuously switch gears so that you don't add stress to your muscles.
b. pedal as quickly as possible when attempting to go uphill.
c. make sure that the positions of the bike seat and handles are appropriate for your height.
d. bike only during the morning hours.

that is correct.

fluid balance is an aspect of the homeostasis of organisms in which the amount of water in the organism needs to be controlled, via osmoregulation and behavior, such that the concentrations of electrolytes (salts in solution) in the various body fluids are kept within healthy ranges. the core principle of fluid balance is that the amount of water lost from the body must equal the amount of water taken in.