The answer is number 5: defends the body against pathogens. Red blood cells do not defend the body, white blood cells do. Red blood cells' purpose is to carry oxygen to the rest of our body.
Answer:
Because capillaries are only one cell layer thick, they only have a tunica intima. This ultra-thin design allows for the exchange of gases and nutrients through the capillary walls.
The answer is B. you could memorize it by the fact that they both start with B