Why do star clusters make superbubbles? Why do star clusters make superbubbles?

Superbubbles form when the hottest, most massive stars in a cluster explode as supernova within a few hundred thousand years of each other. Their bubbles merge into a giant bubble, called a "superbubble."

Explanation:

if you already have the answer to (a), then just work out how many periods there are in 1 minute, and that's the answer to (c).

i am pretty sure it is c because when people are closer together, they cannot move as freely. picture being in a mostly full elevator, for instance. the people are right next to you, and you can barely move.