Under Inland Rule 35, which signal must a sailing vessel sound in restricted visibility?

Why C is correct

33 CFR §83.35(c) groups sailing vessels with vessels not under command, vessels restricted in ability to maneuver, vessels engaged in fishing, and vessels towing or pushing — all of which sound one prolonged followed by two short blasts at intervals of not more than 2 minutes. One prolonged blast is for a power-driven vessel making way; one prolonged followed by three short blasts is for a vessel being towed.