The sentence that uses a modifier correctly is sentence C.
Explanation:
A, B, and D contain misplaced modifiers that make the sentences sound odd. In A, the PP "at summer camp" in final position in the sentence makes it look as if the video was about polar bears which were spending some time at a summer camp. Then, the PP after the participle phrase in B modifies the noun "the dog", so the sentence is understood as if the one with the bathrobe was the dog. Finally, in D, the position of the participle phrase also makes the sentence sound odd. It seems as if the the people saw fires in the air, flying over the forest. Yet, what the sentence logically means is that these people must have been the ones flying over the forest, not the fires. Therefore, the participle phrase should be placed in initial position in the sentence to fix the error.
