An intermediate is an unstable and short-lived molecule in a reaction which is formed in between the reaction when reactants change into products.
Whereas, transition state is just the state before formation of a new molecule. A<span>n intermediate differs from a transition state in that the intermediate has a discrete lifetime. A transition state last for just one bond vibration cycle. Intermediates may be highly stable or unstable molecules.</span>
The use of the prepositional phrase is "on the roof".
On is a preposition and the phrase ends at roof.
I hope that helped!
I belive it is D. good luck with homework