The participial phrase is "crunching" (popcorn), and it modifies "girl".
Explanation:
parallelism means that the same from of words is used in the entire group of words.
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Answer:
What keeps humans motivated on a regular basis.
Explanation:
depending on what you want to have a main focus on for the last part of the sentence you can change.
example
what keeps humans motivated to go to the gym
what keeps humans motivated to continue on in school.