The German use of caused tension to increase between the United States and Germany.
A.
atomic bombs
B.
isolationism
C.
submarine warfare
D.
rationing

An air mass is a large air body that exhibits uniform characteristics of temperature and moisture and helps to decide the weather within a region. In warm-temperature regions of the tropics and sub-tropics, warm air masses appear to form over oceans, while in cold-weather regions nearest the poles, cold air masses tend to form over land. If they travel over warmer or colder land surfaces that experience various forms of air, these air masses may undergo incremental, but substantial, changes. Such boundary lines are known as fronts.

When a cool air mass transitions into hot air, cold fronts exist. Since cold air is heavier than warm air, a wedge is formed by the incoming colder air that displaces the surface's warm, and mostly damp, air. As the warm moist air rises, towering clouds also form the release of energy of strong winds and lightning in the form of short, violent rain storms. Warm fronts, on the other side, can travel up and over cold air at the surface. Clouds and rain can also be caused by these fronts, but they appear to be less aggressive and longer lasting.

How much the air weighs in a given space determines the air pressure. Pressure varies with altitude, with lower altitudes being in denser air and higher altitudes being in lighter air. This is caused by the gravity of the Earth. Its power decreases more away from the center of the globe, because with the same volume of space it binds less molecules together. It warms as the air descends, inhibiting the development of clouds that are also synonymous with good weather. Air increases in environments where the surface pressure is low. The weather cools as it rises and the moisture condenses to create clouds and precipitation. Areas with low pressure are the centres of all hurricanes, so low pressure is also associated with poor weather.

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