The correct answer is D) may be used individually or in conjunction with other distress signals. The explanation is as follows: A distress signal is used to indicate that a vessel or person is in grave and imminent danger and requires immediate assistance. According to maritime regulations, a distress signal can consist of various methods, including visual signals (e.g., waving a large white flag), audible signals (e.g., 5 or more short blasts on a fog signal), and radio signals. Distress signals are often used in combination to increase the chances of being noticed and receiving help. Therefore, answer D is correct as it accurately describes how a distress signal can be used. The other answer choices are incorrect because they do not fully capture the nature and usage of distress signals. Option A describes only one type of visual distress signal, while option B refers to signaling doubt about another vessel's intentions, which is not the purpose of a distress signal. Option C describes a specific audible distress signal, but it does not acknowledge that distress signals can be used in other ways as well.