Which type of air mass is responsible for most of the precipitation in the eastern two-thirds of the united states?

mT air mass.

Explanation:

The maritime tropical air mass comes from the subtropical Atlantic and reaches us in the form of southwest advections. It is a very moist and warm-warm air mass, depending on the time of the year in which it affects us. It is the one that causes the great rain storms of Atlantic origin. It has a variety, the marine subtropical, which comes from the Azores Islands and therefore with more western component. It is something cooler but also very wet.