The correct answer is: C. Specialist
A specialist is an exchange member who is assigned to a specific trading post and is responsible for maintaining a fair and orderly market in a particular security. They do this by buying and selling the security for their own account, as well as by acting as an intermediary between buyers and sellers.
A commission broker is a member of an exchange who executes orders for customers on a commission basis. They do not own the securities they trade, and they are not responsible for maintaining a fair and orderly market.
A floor trader is a member of an exchange who trades for their own account. They are not responsible for maintaining a fair and orderly market, and they do not execute orders for customers.
A dealer is a member of an exchange who buys and sells securities for their own account. They are not responsible for maintaining a fair and orderly market, and they do not execute orders for customers.