Answer the following question given this paragraph: 

Most air masses form over polar or tropical regions. They may form over continents or oceans. Air masses are moist if they form over oceans. They are dry if they form over continents. Air masses that form over oceans are called maritime air masses. Those that form over continents are called continental air masses. Figure below shows air masses that form over or near North America.


Q: Most air masses form over what two types of regions?

 Choices:

- arctic and marine

- polar and arctic

- marine and tropical

- polar and tropical

A:
polar and tropical
