A professional and effective teacher responds to a student's learning difficulties with support, not punishment.
Options (A) and (D) involve punishment, which is counterproductive and harmful.
Option (B), writing the concept repeatedly, is a form of rote memorization that does not guarantee understanding.
Option (C), suggesting a remedial class, is the correct educational approach. Remedial instruction is specifically designed to diagnose and address learning gaps in a supportive manner.
It provides the targeted help the student needs to catch up and understand the concept properly.