Thermal expansion happens when

The coefficient of thermal expansion describes how the size of an object changes with a change in temperature. ... In general, substances expand or contract when their temperature changes, with expansion or contraction occurring in all directions.

the size of an object changes with a change in temperature.

Explanation:

the population of unionid mussels in the hudson river decreased after zebra mussels were introduced. zebra mussels, a nonnative species, competed with the unionid mussels for food. the zebra mussels were able to outcompete the unionid mussels, allowing the zebra mussel population to increase dramatically over six years. the unionid mussel population decreased due to a lack of food.

hope this :

its b it was a compound