The trachea, also known as the windpipe, is a straight tube that extends from the larynx to the anterior part of the thoracic cavity. It is about 4-5 inches long and approximately 1 inch in diameter. The trachea is a crucial part of the respiratory system, providing the passage for air to enter and exit the lungs. The walls of the trachea are supported by C-shaped rings of cartilage, which prevent the trachea from collapsing and blocking the airway. Therefore, option D is the correct answer.