根据短文内容，从短文后的选项中选出能填入空白处的最佳选项。选项中有两项为多余选项。
What is a yawn（哈欠） and why do people yawn? A yawn is often associated with a person being tired．小题1: People yawn for many reasons including stress, boredom, emotion and overwork．
Have you noticed that yawning seems to be contagious （会传染的）? If one person yawns, this appears to cause another person to yawn．Researchers have found that 40-60% of people who see a picture of someone yawning will yawn themselves．小题2:
Some people think that yawning is rude and suggests that you are bored or uninterested．Maybe a yawn is a signal to a group that it’s time to go to sleep, or if someone yawns when they’re bored, it may be a sign to change the topic of conversation．小题3:Animals of all types yawn．If you have a dog or cat, you’ve probably seen your pet yawn several times．Even some birds yawn such as cockatiel parrots, Adelie penguins and Emperor penguins．
Some of the scientific explanations of why we yawn claim it is caused by physical needs．One likely explanation is that the yawning reflex happens when our blood needs more oxygen．The deep breath helps supply the levels of oxygen in our blood．小题4:It is also thought that the same chemicals in our brain that affect our moods and emotions cause us to yawn．
Superstitions about yawning have been around for hundreds of years and can date back to the ancient Greeks．A common superstition says that a person must cover his or her mouth when yawning so that the soul does not escape through the mouth．小题5: Today most people do not believe these superstitions and know that a yawn is a physical reflex．
A．Did you yawn while reading this article?
B．Yawning is not limited to humans．
C．It will make you lose interest in your work．
D．But this is not always the cause for a yawn． E．Even reading the word YAWN can make people yawn．
F．However, it doesn’t mean that you need rest or relaxation．
G．Other people believe that yawning is a sign that danger is near．
H．Another common theory is that a yawn helps regulate our body temperature．
