The correct answer is A) Both methods protect the security of the presentation, but a digital signature has a private and a public aspect. This answer compares both methods but as well provides the main difference between the two of them.
An electronic signature could be any symbol, image or process attached to the document that represents the signer's identity while the password often ends up being forgotten by the signer and most of the time there's no way to recover it.
Hope this helps!