Question

the main, or central, idea of the passage is fevers are useful because they help the body fight infections. how does the detail in bold develop the main idea?
fevers can be uncomfortable, but the upside is that they are evidence of the body’s attempt to heal. when a person develops an infection, a section of the brain called the hypothalamus recognizes a threat. the hypothalamus responds by increasing the body’s temperature. since both viruses and bacteria are temperature sensitive, this environment helps prevent them from multiplying. in addition, scientists have found evidence that fevers may increase the number of certain lymphocytes—white blood cells that are part of the immune system. increased lymphocytes make the body more effective in destroying infected cells. of course, this doesn’t mean that high fevers don’t warrant medical treatment. in fact, another reason that fevers are beneficial is that they serve as warning signs, indicating that something is amiss.
it points out a weakness of the fever response.
it describes one manner in which fevers fight infections.
it explains the function of lymphocytes in great detail.

Explanation:

The bolded main idea states fevers are useful for fighting infections. The passage details this by first explaining that raised body temperature slows the multiplication of temperature-sensitive viruses and bacteria. Then it adds that fevers boost immune cell counts (lymphocytes) to better destroy infected cells, and also notes fevers act as warning signs. All these points elaborate on how fevers actively fight infections.

Answer:

It describes one manner in which fevers fight infections.