Review the item:
Unaware that his alarm clock had not
rung, Levi slept under
warm blankets while Professor Ribley tought
the semester's most difficult algebra concept to the students who had
arrived to class.
The third verb, tought, is the problem. This sentence requires the simple past. Teach is an irregular verb; taught is the correctly spelled form.
| Verb | Simple Present |
Simple Past |
Past Participle |
|---|---|---|---|
| teach | teach(es) | taught | taught |
Had rung (not is an adverb), your choice, is perfectly correct. Before you continue, review the rules for irregular verbs.