This is the only answer with incorrect grammar. I'm guessing that the underlined portion is "path and paved." All of the other answers work in a sentence.
It just doesn't make sense when you say this: "The county cleared this path paved it with packed gravel, so they would have a peaceful place to hike and bike."
It's missing an "and" to separate the independent and dependent clauses.
Answer: You should keep school environment clean because a clean enviroment is a healthy enviroment. It also sets an example for future students joining the school.
