Question

the main, or central, idea of the passage is the flu and the stomach flu are separate conditions, each with its own causes and symptoms. how does the detail in bold develop the main idea? though proven effective in flu prevention, the influenza vaccine, or \flu shot,\ wont keep you from contracting the stomach flu. this is because the name \stomach flu\ refers to a condition that is completely different from the ordinary flu, or influenza. in common parlance, \stomach flu\ typically refers to a condition called gastroenteritis, in which the digestive tract becomes irritated. there is no vaccine to prevent gastroenteritis, which may be caused by a variety of viruses, bacteria, other organisms, and certain foods. common symptoms include stomach pain, vomiting, and diarrhea. the
egular\ flu, on the other hand, results from a strain of the influenza virus. common symptoms include fever, cough, congestion, fatigue, and muscle aches. stomach upset may also occur, but this is not as common as the other symptoms. it compares the symptoms of influenza and the stomach flu. it supports the writers argument for a stomach flu vaccine. it addresses a common misconception about the flu shot.

Explanation:

The bolded detail "Though proven effective in flu prevention, the influenza vaccine, or 'flu shot,' won't keep you from contracting the stomach flu" addresses a common misconception. Many might assume that the flu shot protects against all types of "flu - like" illnesses. But this statement clarifies that the flu shot (for influenza) has no effect on the stomach flu (gastroenteritis). It doesn't compare symptoms (as the symptom comparison comes later in the text). Also, there is no argument for a stomach flu vaccine in the passage.

Answer:

It addresses a common misconception about the flu shot.