Because of the way builds up in your body
Different types of blood contact different kinds of antigens and antibodies. For example, Type A blood has A antigens and B antibodies, antibodies being the thing that fights B antigens. Type B blood has B antigens and A antibodies. So if someone with type B gets transfused with Type A blood, the person's antibodies will attack the new blood.
Answer: Fitness or camouflage
Explanation: C and D don’t make any sense
Every person has their own part to play or if you want to get scientific then a niche. And if somebody doesn't do their job then it could slow everyone else down. Maybe I don't fully understand the question, But I hope its right.
