A hormone is a secreted molecule that is carried in the bloodstream to where it acts on target cells that bear specific receptors for that hormone.

The antibodies produced in allergic reactions belong to the immunoglobulin E group.
These antibodies bind to an allergen, triggering a release of histamine, which causes allergy symptoms.
They also help to fight parasitic infections.
Choice B is wrong because allergens are not antibodies, but substances that cause an allergic reaction.
Choice C is wrong because the antibodies that belong to the immunoglobulin G group are not involved in allergic reactions, but in fighting bacterial and viral infections.
Choice D is wrong because mast cells are not antibodies, but cells that release histamine and other chemicals when activated by IgE antibodies.

A person with type AB blood can successfully receive blood from all blood types.
This is because type AB blood has both A and B antigens on the surface of red blood cells, and therefore does not have antibodies against either antigen in the plasma.
Type AB blood is also called the universal recipient.
Choice B is wrong because type AB blood can receive more than just type O blood.
Type O blood is the universal donor, meaning it can be given to anyone, regardless of their blood type.
Choice C is wrong because type AB blood can receive more than just two of the blood types. Type AB blood can receive both A and B blood, as well as O and AB blood.
Choice D is wrong because type AB blood can receive more than just one of the blood types. Type AB blood can receive any blood type without problems.
Normal ranges for blood types vary by population, but generally, type O is the most common, followed by type A, type B, and type AB.