Acovalent bond is a chemical bond in which atoms share an isotope. a nucleus. molecules. electrons.

The answer is electrons. 

A covalent bond is a type of chemical bond where atoms share electrons.  Covalent bonds are also referred to as molecular bonds because they form molecules when bonded.

This type of bond occurs between non-metals. An example of a compound or a molecule that is formed through covalent bonding is water. It is a combination of two hydrogen atoms bonded with an oxygen atom. H₂O 

Mis useing driving his or her license will be suspended for one year

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)