The answer is C. streamers and balloons because it has the conjunction and in the subject and is talking about 2 nouns in the subject, making it a compound subject.
I recently went on a scavenger hunt at the yorktown mall with a bunch of friends. It was really fun cuz we ate, shopped, and celebrated one of my friends birthday.
Hope this helped!
C. Theme
The next closest is D. Plot, but since it's an 'idea', it's theme
to persuade the reader that the Grimm brothers were influential