The correct answer is D. Unearned revenue.
Unearned revenue is revenue that a company has received but not yet earned. It is a liability because the company has an obligation to provide goods or services in the future in exchange for the revenue that it has received.
Accrued expenses are expenses that have been incurred but not yet paid. They are a liability because the company has an obligation to pay for the goods or services that it has received.
Contra asset revenue is a type of revenue that is offset by an expense. It is a contra asset because it reduces the amount of revenue that is reported on the income statement.
Accrued revenue is not a contra asset because it is not an expense. It is a liability because the company has an obligation to provide goods or services in the future in exchange for the revenue that it has received.