Answer:
C. How on Earth, Jenny thought, could the concert have already started when she had left an hour early?
Step-by-step explanation:
This is the answer because, it says that "Jenny thought" and if it was using a 1st person point of view it would simply say "I thought". And it also says that when "she" had left an hour early. If it was a 1st person point of view it would also simply say "I". And it couldn't be option A, because it said "we" when the sentence (if it was trying to be in third person) should've used "they".
It can't have been option B, because it says, "in my experience" and if you were writing it in first person it would have been "in their experience", or "in (name)'s experience".
It also couldn't have been option D. Simply because it says, "As for me" and uses "I" instead of they, she, he, or even their name.
To make it short, option A, B, and D, do not have the correct wording to be a third-person sentence.
So, in conclusion, the only third-person sentence is option C.
And that's my answer.