A colon is mostly used to show that you are going to make a list of things after the comma. So, having that in mind, the correct answer is the first option - I edited the article and found: comma splices, sentence fragments, and misplaced modifiers.
You listed three things here, therefore you have to put a colon. If you are going to mention only one thing, like in the other examples, a colon is not needed.
Is there any picture or answer choices we can choose from? We cannot help you if you do not provide us with this stuff. I can help if you give me them.
I would say A, but I'm not sure.
The large group is excited about the upcoming event.
