Take a look at the sentence again:
Unaware that his alarm clock had not rung
at 6 a.m., Levi slept under the warm blankets
while Dr. Ribley tought the semester's most
difficult algebra concept to the students who had arrived on time.
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.
Try again to become a champion!