Final answer:
The intensive pronoun that completes the sentence 'Evelyn and I finished an entire pizza' is 'ourselves', emphasizing the subjects.
Step-by-step explanation:
The intensive pronoun that completes the sentence 'Evelyn and I finished an entire pizza' is 'ourselves'. This form of pronoun is used to emphasize the subjects (Evelyn and I) who performed the action of the verb (finished). Intensive pronouns are reflective pronouns that are not essential to the completeness of the sentence, meaning the sentence would still make sense if the intensive pronoun were removed.