4. into
5. at
6. in
7. no preposition
Prepositions tell the relation of one noun or pronoun to another. For example, in sentence 5 "at" gives the relation of the trail to the beginning. There is no preposition in sentence 7.
8. and
9. so
Conjunctions join words together. In sentence 8, the conjunction, and, joins Earth's two actions (rotates, revolves). In sentence 9, the conjunction, so, joins the description of Neptune's color to the reason for its name. The word "for" in sentence 9 is being used as a preposition, not a conjunction. Sentence 7 has a conjunction - but. It joins together two complete sentences.