Question

connections and transitions quick check
\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, said 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 neuroethicist 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 lungs, helping the body to liven 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 point out a specific example of a general phenomenon
to draw a contrast between two ideas
to show a cause/effect relationship
to group together explanations to the same question

Explanation:

The text presents multiple theories about why we yawn. "One theory" starts to introduce an explanation and "other proposals" continues to list more explanations for the same question of why we yawn.

Answer:

to group together explanations to the same question