Read the passage. (1)Ever realized how yawns seem to be “contagious?” Even if you try to cover your mouth when you yawn, chances are good that at least one other person around you will “catch” your yawn and yawn right along with you. What's the deal with all that yawning?

(2)Dr. William Broughton, director of the Sleep Disorders Center at the University of South Alabama Knollwood Hospital, says that contagious yawning is programmed into us. According to Dr. Broughton, contagious yawns are a response built into most people. Studies have shown that many people who watch videos of other people yawning—or even hear talk about yawning—end up doing the same.

(3)Researchers from the State University of New York in Albany tested people to find out why many people are likely to “catch” a yawn from someone else. Through their research, they found that people who are very aware of themselves and their surroundings are more likely to catch yawns. In other words, if you think your friend might be yawning out of boredom, you might yawn, too, to show your friend that you understand how he or she is feeling.

(4 )Dr. Broughton also notes contagious yawning might be a kind of “habit” left over from ancient times, when yawning allowed groups of humans to coordinate their times of sleep. When ancestral humans lived in troops, it was important for them to wake up at the same time. Yawning may have been a way for them to communicate the level of alertness among different group members, say some scientists.

(5)Other research has been done that says we don't yawn because we are tired. People used to think humans yawned to increase oxygen levels in the blood, but that may not be true. We may yawn when we are drowsy because stretching motions increase heart rate. The yawn may just be a stretch of the mouth and throat.

(6)Whether yawning is programmed into our brains, a learned social behavior, or a freak habit of humans, watch out: it's catching!

"Yawning It's Catching!".

Which sentence best summarizes paragraph 4?

A

Scientists have disproved the idea that we yawn because we are tired.

B

Contagious yawning might be a social phenomenon, according to scientists like Dr. Broughton.

C

Ancestral humans used to live in troops.

D

Yawning may be an ancient “habit” that formed when humans needed to sleep and wake up at the same time.

JUST PLEASE HURRY!