Question

flu confusion
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.
what is the main, or central, idea of the passage?
the flu and the stomach flu are separate conditions, each with its own causes and symptoms.
while flu shots can help prevent influenza, they do not prevent gastroenteritis, or stomach flu.
the term \stomach flu\ is more correctly known as gastroenteritis, in which the digestive tract becomes irritated.

Explanation:

The passage first mentions that the flu shot doesn't prevent stomach flu. Then it explains that "stomach flu" (gastroenteritis) is different from the regular flu (influenza). It details their causes (various organisms and foods for gastroenteritis, influenza virus for regular flu) and symptoms (stomach - related for gastroenteritis, fever - cough - etc. for regular flu). The main idea should cover the separation of these two conditions.

Answer:

The flu and the stomach flu are separate conditions, each with its own causes and symptoms.