It can't be letter A because the title character is not Clerval.
It can't be letter B because the title character is also not the professor nor his colleague.
It could be letter C is not the title character. It most likely is about Frankenstein's monster, not himself.
Considering all that, the answer must be letter D.
"Before this, I was not unacquainted with the more obvious laws of electricity."
Frankenstein had to become a little more familiar with electricity to create his monster, since it's know that he electrocutes the mounted body in order to make it live.
