The correct answer is A) readily accessible for transfer to a lifeboat. This is the correct answer because the required portable radio on a vessel must be stored in a location where it can be easily accessed and transferred to a lifeboat in an emergency situation. The radio needs to be readily available for use in the lifeboat, which is the primary purpose of this requirement. The other answer choices are incorrect because they do not address the requirement for the radio to be readily accessible for transfer to a lifeboat. While the radio should be equipped with an approved carrying case (B) and spare batteries (C), and stored in a waterproof enclosure (D), these are secondary considerations compared to the primary requirement of ensuring the radio can be quickly accessed and transferred to a lifeboat.