The correct answer is: C. Rung : Ladder
A sedan is a type of automobile. A rung is a step on a ladder. In both cases, the first word is a part of the second word.
Marble is a type of stone. A statue is a sculpture. In this case, the first word is not a part of the second word.
A rocker is a type of chair. In this case, the first word is not a part of the second word.
A hanger is a device for hanging clothes. An aeroplane is a type of aircraft. In this case, the first word is not a part of the second word.