Which matter is left uncertain in this excerpt?

Question

(1 point)
Responses

the exact scientific reason for yawning
the exact scientific reason for yawning

the chemicals that make up “yawn gates”
the chemicals that make up “yawn gates”

the reason that yawns are a special kind of respiration
the reason that yawns are a special kind of respiration

the idea that yawns involve the muscles of the face

Answer 1

The uncertain matter in the excerpt is "the exact scientific reason for yawning."