In the bell jar model, the Y-tube arms represented the: a. diaphragm. b. bronchi. c. lungs. d. trachea.

The correct answer is (b) bronchi. In the bell jar model, the Y-tube arms represent the bronchi because they are the two primary branches that carry air from the trachea into the lungs. The diaphragm is represented by a rubber sheet at the bottom of the bell jar and is used to simulate inhalation and exhalation. The lungs themselves are not directly represented in the model, as they are the organs within the body that actually exchange gases with the bloodstream.