Read the passage from When Birds Get Flu by John DiConsiglio. It was September 2004. An 11-year-old girl had fallen ill after playing with some sick chickens. At first, it seemed like a bad case of the flu. But the girl kept getting sicker.

In the hospital, her mother held her for hours. Then early in the morning, the girl died. Soon, her mother began to feel sick. The mother died, too.

Dr. Dowell is an epidemiologist. His job is to figure out what makes people sick—and to keep diseases from spreading to others. He feared that the little girl and her mother had died from a rare bird flu.

If Dowell was right, it could mean big trouble.

Which statement best explains the central idea that this passage introduces?

Dr. Dowell will try to keep the flu from making others sick.
Dr. Dowell will try to find out if the girl and her mother died of bird flu.
Dr. Dowell will investigate whether the hospital did something wrong.
Dr. Dowell will investigate the chickens that the girl was playing with.