Answer: D. face-to-face exams
Explanation:
Out of the options listed, a face-to-face exam is the best option and indeed an actual method used for authentication by instructors.
The idea is that if indeed it is your work, you should be so well versed in it that you could pass an examination based on the intricacies of the work. The instructor sets a grade percentage that you must pass usually on the first try to prove that indeed, the work is your own.
