The correct answer is B) cPk. The symbols used to represent air masses are based on their source region and the degree of modification that has occurred as the air mass moves. The symbol "c" represents a continental air mass, while the symbol "m" represents a maritime air mass. The suffix "P" indicates a polar air mass, while the suffix "T" indicates a tropical air mass. In this case, an air mass that has moved down from Canada would be a continental polar (cP) air mass, which is correctly represented by the symbol cPk.