Explanation:

- Diaphragm: The correct answer. Hiccups are caused by involuntary contractions of the diaphragm, a muscle that separates the chest from the abdomen. This muscle helps in breathing, moving downward with inhalation and upward with exhalation. During hiccups, the diaphragm contracts suddenly.

- Trachea: This is the windpipe providing air passage to the lungs. It is not directly involved in causing hiccups.

- Lungs: These organs facilitate gas exchange, but they do not cause hiccups. They are affected by the diaphragm's movement.

- Larynx: Known as the voice box, it is involved in breathing, producing sound, and protecting the trachea, but not in causing hiccups.