Read the following excerpt from a bigger passage.

from Yawning Together by Dave Munger

• Most yawns last about six seconds.

• While the majority of the 58,000 species of vertebrates yawn, only humans, chimpanzees,
and dogs appear to find them contagious.

• Humans are capable of yawning as young as 11 weeks after conception—before they are
even born!

• Yawns become contagious in humans between the first and second years of life.

• While yawns are commonly associated with boredom or fatigue, your heart rate actually
increases during a yawn—by as much as 30%.

What is the primary purpose of the article?
A) To summarize research on contagious yawning
B) To explain why yawning is healthful for people and animals
C) To describe how human yawning differs from dog yawning
D) To suggest that scientists will never fully understand why people yawn