Mononucleosis, or "mono" for short, is an infectious disease usually caused by the Epstein-Barr virus. This virus is transmitted through saliva, so mono can be spread
through kissing, coughing, sneezing, and sharing straws or utensils. Symptoms may
include fever, sore throat, fatigue, weakness, and swollen lymph nodes in the neck or
underarms. A doctor may need to do a blood test to confirm a diagnosis of mono.
Symptoms usually go away on their own within a few weeks, but some patients continue
to experience fatigue and weakness for several months.
Which author's purpose is suggested by the text?
to inform readers about the discovery of the Epstein-Barr virus
to describe how it feels to have mononucleosis
to inform readers about an infectious disease called mononucleosis

The author's purpose suggested by the text is:

C. to inform readers about an infectious disease called mononucleosis.

Explanation:

Let's summarize the passage by dividing it into topics:

- there is a disease called mononucleosis;

- the virus that causes it is the Epstein-Barr;

- it spreads through saliva;

- the symptoms include fatigue, fever, sore throat, etc.;

- a blood test can confirm the disease;

- the symptoms last a few weeks.

As we can see, the passage gives us some general knowledge about the disease. It does not focus on how the virus was discovered at all. Even though it mentions the symptoms of mono, it is incorrect to say that the passage's purpose is to describe how it feels to have the disease. That is not its focus, it is just one of the many topics it discusses. Therefore, the best option is letter C:

C. to inform readers about an infectious disease called mononucleosis.

that is true because that is something they fulfill for their work.