Question

why are yawns contagious? we asked a scientist by teresa carey
there is no scientific consensus on why we yawn.
one theory argues that when humans are tired, we stop taking deep breaths, which causes a build - up of carbon dioxide in the body. sand douglas parham, a speech scientist at wichita state university. a yawn might be a special kind of respiration. parham said it builds up oxygen quickly, while expelling carbon dioxide, even more than a deep breath.
excess carbon dioxide and other chemical changes, such as a drop in oxygen or increase in a compound called adenosine, could also act as yawn gates, said james giordano, a neurobiologist and neuroscientist at georgetown university. these chemicals send out a signal that triggers a yawn. by yawning, we compress the muscles of the face, driving oxygen - enriched blood to the brain, giordano said.
other proposals state the purpose of yawning is to cool the brain, or to stretch internal organs like tissues and ligaments, helping the body to loosen up.
use the passage to answer the question.
what is the purpose of the transitions one theory and other proposals in this excerpt? (1 point)
○ to show a cause - effect relationship
○ to point out a specific example of a general phenomenon
○ to draw a contrast between two ideas
○ to group together explanations to the same question

Explanation:

The transitions "One theory" and "other proposals" are used to group together different explanations regarding the same question of why yawning occurs. They are not used to draw a contrast, point out a specific example, or show a cause - effect relationship.

Answer:

to group together explanations to the same question