Choose the best answer: If you breath in deeply, your ........... can expand to twice their normal size

Choose the best answer:
1. If you breath in deeply, your ...................... can expand to twice their normal size.
A.lung                 B. stomach                      C. heart                       D. brain
2. ..................... system is made up of our bones. It supports our body and protect our organs.
A. Circulatory              B. Digestive               C. Nervous                   D. skeletal
3. This system of the body lets us breathe in oxygen with our ............. and breathe out carbon dioxide.
A. heart                        B. lungs                     C. brain                           D. intestine