Detailed Instructions: You are given a paragraph, a question and some answer options (associated with "A", "B", "C", "D", etc.) You need to list all the correct answer options with their associated letters (e.g. "A" can be a valid answer). Note that sometimes, more than one option can answer the question correctly and completely. In those cases, please generate all such options separated by a comma (e.g. "A, B" is a valid answer). Do not generate anything else apart from one or more of the following characters: 'A', 'B, 'C', 'D', etc.
Q: Paragraph- Sent 1: Breathing is the process of moving air into and out of the lungs.
Sent 2: The process depends on a muscle called the diaphragm.
Sent 3: This is a large, sheet-like muscle below the lungs.
Sent 4: Inhaling, or breathing in, occurs when the diaphragm muscle tightens.
Sent 5: This increases the size of the chest.
Sent 6: This too decreases air pressure inside the lungs.
Sent 7: This action allows air and gases to enter the lungs.
Sent 8: Exhaling, or breathing out, occurs when the diaphragm muscle relaxes.
Sent 9: This decreases the size of the chest.
Sent 10: This increases air pressure inside the lungs.
Sent 11: This action allows for air to leave the lungs.
Sent 12: When you inhale, air enters the respiratory system through your nose and ends up in your lungs, where gas exchange with the blood takes place.
Sent 13: What happens to the air along the way?
Sent 14: In the nose, mucus and hairs trap any dust or other particles in the air.
Sent 15: The air is also warmed and moistened.
Sent 16: Next, air passes through a passageway that is connected to the windpipe.
Sent 17: The air then finds its way to the lungs.
Sent 18: In the chest, the windpipe splits so that air enters both the right and left lung. 
Question: The nose, diaphragm, lungs, and windpipe are all a part of what system in our body? (A) Digestive system (B) Respiratory System.
A:
B.