Sentence Correction

The below example may be helpful for 1st question..

1. As your brother, I must warn you to be careful(iam your brother)
2. Like your brother, I must warn you to be careful(iam not your brother, but he and I have similar attitudes)

>>>> humingbirds (like/as) insects

For question 4. I only found incidental to, but didn't find either incidental from or incidental of.
So I don't know whey E is wrong.