What is an air mass and how
can you tell them apart?

An air mass is a body of air with a relatively constant temperature and moisture content over a significant altitude. Air masses typically cover hundreds, thousands, or millions of square kilometers. A front is the boundary at which two air masses of different temperature and moisture content meet.  Meteorologists identify air masses according to where they form over the Earth. There are four categories for air masses: arctic, tropical, polar and equatorial. Arctic air masses form in the Arctic region and are very cold. Tropical air masses form in low-latitude areas and are moderately warm.

Explanation: Maritime tropical air masses (mT), for example, develop over the subtropical oceans and transport heat and moisture northward into the U.S.. In contrast, continental polar air masses (cP), which originate over the northern plains of Canada, transport colder and drier air southward.

the answer is b.) hydrogen bonds between bases.