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.