BOTH INTERNATIONAL & INLAND Signals required for vessels aground include __________.

Correct Answer: Option C — by day, three black balls in a vertical line

Rule 30(d)(ii) mandates that a vessel aground must exhibit three black balls in a vertical line during the day. At night, Rule 30(d)(i) requires two (not three) all-round red lights in a vertical line in addition to the standard anchor lights, making option C the only correct choice.