The warm, moist air masses in the tropics in the atmosphere as they heat.

sink

rise

circulate

none of the above

Option (b) is the correct  answer.

Explanation:

When air is warmer then it means it molecules are moving rapidly from its initial place. Hence, its molecules gain more kinetic energy due to which there occurs more number of collisions between its molecules.

As a result, these molecules move farther apart from each other leading to the rise of air molecules.

Thus, we can conclude that the warm, moist air masses in the tropics rise in the atmosphere as they heat.