In the first question, you need the conjunction. You cannot change 'go' to 'attend' as it will not make sense. Neither cannot be replaced by 'either', so that leaves you with one choice, and that is Choice C.
In the second question, a dependent clause is a group of words that cannot stand by itself. I believe the answer for this second questions would be D, because you can't find a group of words that cannot stand by itself.
In the last question, an independent clause is a group of words that can stand by itself. The group of words that can stand by itself in the sentence is I can't find the sweater.
I hope this helped, I got to run. :)
