The correct answer is D) Carbon ring. The carbon ring seal is commonly used in the gearbox of a gas turbine engine. This type of seal is designed to provide an effective and durable sealing solution for the high-speed, high-pressure environment found in gas turbine engines. Carbon ring seals are preferred over other options like lip-type, fishmouth, or labyrinth-windback seals due to their ability to withstand the harsh operating conditions and maintain a reliable seal between the gearbox and the rest of the engine. The other options are not typically used in gas turbine engine gearboxes. Lip-type seals may not provide sufficient sealing performance, fishmouth seals are more common in lower-speed applications, and labyrinth-windback seals are better suited for applications with lower pressure differentials.