Answer: B.
Step-by-step explanation:
cant be 'A' cause carbon 14 is found in any living organism and mammals are not the only living organism on this planet
cant be 'C' cause ancient plants still replenish carbon 14 molecules and it'd be impossible to now its age when its still alive
couldnt be 'D' cause yeah while alive organisms do absorb carbon 14 that still defeats the purpose of dating with the carbon 14 method cause its still also taking in carbon dioxide, so the carbon-14 molecules will just keep filling until the organism dies. the whole point of dating with carbon 14 is to measure its deplenish (dying) not continual replenish (living)
dont know if that makes any sense to you but yeah 'B' is the answer, if it isnt im stoopid but im not