Question

creating lake-effect snow
situated on lake erie, the city of buffalo, new york, is one of the snowiest cities in the
united states. like other cities on large lakes, it is subject to a phenomenon called lake-
effect snow. water retains heat, so lake water is often warmer than the air. in the lake
effect, cold air moves over warmer lake water, initiating a process that can produce large
snowstorms. moisture from the lake evaporates into the cold air, warming it. because
warm air is less dense than cold air, it begins to rise. as it rises and moves away from the
lake, it cools down. as the air cools, moisture condenses and forms into clouds. if the
temperature is cold enough, the moisture falls to the ground as snow.
what is the main, or central, idea of the passage?
when cold air moves over the warmer water of a lake, lake-effect snow can
be produced.
in the lake effect, warm air, which is lighter than cold air, rises and moves
away.
buffalo, new york, gets more snow than most cities in the united states.

Explanation:

The passage starts by introducing Buffalo, NY on Lake Erie and mentions lake - effect snow. Then it explains the process: cold air over warm lake water (evaporation, warming air, rising, cooling, condensation, snow if cold enough). The first option summarizes the overall process of lake - effect snow formation. The second option is just a part of the process (about warm air rising). The third option is about Buffalo's snow amount which is just an example to introduce the phenomenon, not the main idea.

Answer:

When cold air moves over the warmer water of a lake, lake - effect snow can be produced.