Question

bee stings: the aftermath
you dont have to have a life - threatening allergy to have a negative response to bee stings. many people experience uncomfortable itching and swelling when stung. but are such reactions merely an annoyance, or might they serve a purpose? several years ago, researchers who study the immune system wanted to find out. to do this, they injected a group of mice with bee venom. some of the mice had allergic reactions (such as swelling) to the venom, and others did not. three weeks later, the researchers injected the same mice with venom for a second time - this time with a dose so large it could be deadly. they found that the mice who had previously had allergic reactions to the venom were much more likely to survive the potentially lethal dose.
what is the main, or central, idea of the passage?
researchers found that allergic reactions to bee venom can be as mild as swelling or as severe as death.
researchers found that mild allergic reactions may help prevent severe reactions to the same allergen in the future.
researchers found that bee venom causes allergic reactions in some mice but not in others.

Explanation:

The passage describes an experiment where mice with previous mild allergic reactions to bee venom were more likely to survive a later, potentially - lethal dose. This indicates that mild allergic reactions may have a protective effect against future severe reactions to the same allergen.

Answer:

Researchers found that mild allergic reactions may help prevent severe reactions to the same allergen in the future.