I have taught in high school for ten years. In that time I have given assignments to many students, including a murderer, an evangelist, a boxer, a thief, and an imbecile. The murderer was a quiet, little boy who sat on the front seat and looked at me with pale blue eyes. The evangelist, easily the most popular boy in the school, had the lead in the junior play. The boxer lounged by the window and let loose at intervals with a raucous laugh that startled even the geraniums. The thief was a gay-hearted soul with a song on his lips. And the imbecile was a soft-eyed little fellow who preferred to remain unnoticed.

All of these pupils once sat in my room, sat and looked gravely across worn, brown desks. I must have been a great help to these boys. I taught them the rhyming scheme of the Elizabethan sonnet and how to diagram a complex sentence.

Q. Underline the sentence which suggests that the narrator is an experienced teacher.