Concept:Cracking occurs due to uneven thermal expansion between the inner and outer surfaces of the glass.Explanation:When boiling water is poured into the tumbler, the inner surface heats up quickly.The inner surface expands rapidly as its temperature rises.The outer surface remains relatively cool and expands more slowly.This difference in expansion rates produces internal stress within the glass.Since glass is brittle, the stress exceeds its strength and causes it to crack.Answer:A. The inside expands more rapidly than the outside.