What is the main function of Red Blood Cells (RBC) in human blood?

The main function of white blood cells is –

If the red blood cells (RBCs) of human blood are isolated and are diluted in normal saline (an isotonic solution to blood), what will happen to the RBCs?

What function does blood perform in the body?

Life span of red blood cells is _____ days.

In which part of our body are Red Blood Cells (RBCs) formed?