Question

Which matter is left uncertain in this excerpt?the idea that yawns involve the muscles of the facethe idea that yawns involve the muscles of the face• the chemicals that make up "yawn gates"
the idea that yawns involve the muscles of the face
the reason that yawns are a special kind of respiration

Answer 1

Based on the options provided, the matter left uncertain in the excerpt appears to be "the reason that yawns are a special kind of respiration." The other options are more factual or descriptive, while this one suggests a deeper inquiry into the nature or purpose of yawning that is not clearly explained.