The correct answer is D) Four blasts of the whistle, namely 1 short 2 long and 1 short. This is the correct answer because the International Regulations for Preventing Collisions at Sea (COLREGS) specify that four blasts of the whistle, consisting of one short, two long, and one short blast, is the signal used to indicate that a vessel is complying with a request or instruction from an icebreaker. The other answer choices are incorrect because they do not match the COLREGS requirement for the specific whistle signal to be used in this situation. The code flags "A" (Alpha) and "L" (Lima) have different meanings, and using a series of 3 or 4 blasts without the proper pattern would not correctly signify compliance with the icebreaker's instructions.