Which of the following is a true statement about lake-effect snow?

a) Lake-effect snow is caused when a continental polar air mass from Canada moves over the warmer Great Lakes.

b) Lake-effect snow is caused when an arctic air mass from Canada moves over the warmer Great Lakes.

c) Lake-effect snow is caused when a tropical air mass from the United States moves over the warmer Great Lakes.

d) Lake-effect snow is caused when a continental polar air mass from the United States moves over the warmer Great Lakes.

As the cooler air mass from the NorthWest, from the arctic, moves over the Great lakes in the United States, the air in contact with the lake is warmed up and gathers even more moisture. Because warmer air is less dense than cooler air, it begins to rise. As it rises, it interacts with the upper cooler air of the air mass and begins to cool. The moisture in it condenses and cools into snow that is deposited on the downwind side of the shores of the Great lakes.