The diagram below represents a human organ system the major function of the system is to:

1. Provide immunity essential for survival of each individual in a population.
2. Provide cells that are necessary for the survival of the species.
3. Produce chemical messages are necessary for nerve cell development.
4. Control the passage into and out of a developing fetus.


Please choose the answer for me please. I need help with that question and explain why it is the answer please so I can understand.