Final answer:
A principal residence refers to the primary dwelling where an individual usually lives. All options provided can qualify as a taxpayer's principal residence except a boat.
Step-by-step explanation:
A principal residence refers to the primary dwelling where an individual usually lives. According to the information provided, all of the options given can qualify as a taxpayer's principal residence except a boat (option C). While houses (option A), apartments (option B), and condominiums (option D) are commonly used as permanent residences, boats are typically not considered to be primary dwellings.