Transporting substances in a cell. proteins are transported either in or out of the cell.
The answer you're looking for is C
Answer:
Alveoli
Explain:
They are the workhorses of your respiratory system. You have about 480 million alveoli, located at the end of bronchial tubes. When you breathe in, the alveoli expand to take in oxygen. When you breathe out, the alveoli shrink to expel carbon dioxide.
