Answer:
The sentence in the passage that is a sentence fragment is sentence 4.
Step-by-step explanation:
We can define fragment as a group of words that initially looks like a sentence but that lacks something essential in order to make sense. A fragment can lack, for instance, the subject, or even the predicate.
That is the case with sentence 4: "A dedicated environmentalist himself." What about him? There is no verb, no predicate, nothing. This fragment could become a subject if we added a proper predicate after it. Or, maybe, it is supposed to be an absolute phrase - a phrase that modifies the sentence that follows. But, the way it is now, sentence 4 makes no sense.
A possibility would be replacing the period with a comma and connecting sentences 4 and 5. Notice how that makes more sense:
- A dedicated environmentalist himself, Marco wrote a proposal.