Answer:
b. There is insufficient contrast in surface type (land vs. ocean) in the middle latitudes.
Explanation:
The sources of air masses can be produced or at very high latitudes because they can carry big amounts of air from the top of a mountain till the bottom by the differences of pressure and temperatures. This kind of air mass is called continental.
In the other hand, in a low latitude, the air coming from the sea, try to reach higher latitudes, again, by pressure and temperatures differences. These kind of air masses are called maritime.
Hope it was useful.
