Sometimes the most difficult aspect of training for a new career is finding balance and managing stress. You may have also enrolled in a class that provided an extra challenge for you because the professor moved too quickly or didn't present the information in a clear way. Maybe you struggle to memorize medical terminology. Regardless of the difficulty, explain what it was and then elaborate upon how you handled it. The interviewer is more interested in how you overcame the challenge than the challenge itself! What tools did you use? Did you go to tutoring? Did you meet with the professor during office hours?