Question

read the passage.
bee stings: the aftermath
you dont have to have a life - threatening allergy to have a negative response to beestings. many people experience uncomfortable itching and swelling when stung. but aresuch 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 agroup 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 samemice 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 weremuch 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 asswelling or as severe as death.
researchers found that mild allergic reactions may help prevent severereactions to the same allergen in the future.
researchers found that bee venom causes allergic reactions in some mice butnot in others.

Explanation:

The passage starts by asking if allergic reactions to bee stings (like itching and swelling) are just an annoyance or have a purpose. Then it describes an experiment where mice were injected with bee venom. Some had allergic reactions (like swelling), and when injected again with a potentially deadly dose, those with previous allergic reactions were more likely to survive. This shows that mild allergic reactions (the first - time ones) may help prevent severe (the second - potentially deadly) reactions to the same allergen (bee venom) in the future.
The first option is incorrect because the passage is not mainly about the range of allergic reaction severity (mild to death). The third option is just a detail of the experiment, not the main idea. The main idea is about the role of mild allergic reactions in preventing severe ones in the future.

Answer:

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