use the excerpt to answer the question which matter is left uncertain in this excerpt

Question

a. the exact scientific reason for yawning
b. the idea that yawn involve the muscle of the face
c. the reason that yawns are a special kinf of respiration
d. the chemicals that make up yawn gates

Answer 1

The matter that is left uncertain in the excerpt is:

a. the exact scientific reason for yawning.

This option reflects the ambiguity surrounding the definitive explanation of why yawning occurs.