Why do warm air masses rise when they meet cold air masses?

a. they are less dense
b. they are colder
c. they are denser
d. they have more saturated

Johnny rode his bike 4 blicks down the street to his friend's house once he got to his friend house and realized he could not cone out to play he turned aroubd and went back home.what is displacement for the total bike ride? how did you determine this? what could we use as a reference point to determine he was in motion during his bike ride? why can you use it as a reference point