Bonus plans are not liabilities that need to be estimated because they're contingent payments.
The correct answer is B. bonus plans.
Liabilities that must be estimated are obligations or debts for which the exact amount is uncertain but can be estimated reasonably. Warranties, vacation pay, and promissory notes are examples of liabilities that require estimation because they involve future payments or obligations with uncertain amounts. However, bonus plans are not liabilities that need to be estimated because they are contingent payments that depend on meeting certain criteria or performance targets.