No dictionary has found the best way to explain complete and finish and why we use them differently, though they can usually work in the same sentence if you were to replace one with the other
"Has everyone completed their test?"
"Has everyone finished their test?"
I think it would be vacationing, because it is the subject of the sentence. The only other option would be sewing but since that looks more like an adjective I think vacationing would be the right answer.
The answer would be the first choice or A. "Original ideas that are <em>not</em> your own."
Any piece of information that does not belong to you would require a citation, otherwise it would be considered <em>plagiarism. </em>B and C are incorrect because both of those things belong to you, and therefore don't require citation. D is also incorrect because a general fact doesn't belong to any one person. For example, if you wanted to include the information that dogs can't eat chocolate, that wouldn't require a citation because that is general knowledge that most people are aware of.