The correct answer is C) A canister is reliable for up to 5 years from the date of manufacture, as long as the seal is unbroken. This is correct because gas/filter mask canisters are generally designed to have a service life of up to 5 years, provided the seal remains intact. The other options are incorrect - option A underestimates the protection time, option B is too restrictive, and option D incorrectly combines the other inaccurate statements. As long as the canister seal has not been broken, the chemical filters and absorbents inside remain effective for the manufacturer's stated service life, which is typically around 5 years. Canisters should be replaced once they reach their expiration date or if the seal is compromised, but they do not have a strict 24-hour limit when the seal is unbroken.