Hi,
I was told that something like the one below is an inverted structure, << It seems reasonable to call it that.then what the second one that is underlined?
Among the students signed up for the contest are John and Sam. -- Inverted of "John and Sam are among the students signed up." And this supposed to show the prepositional phrase is not a noun (acting as a subject)? It's just a statement. It isn't supposed to 'show' anything. A simpler form is, for example, In that house lives Tom.
Then what is this? Is this a noun?
One of the best ways is to see them off is with commas. Consider a simpler example. I want to break a window. One of the best ways is to hit it with a hammer. 'With a hammer' is not a noun. It's a prepositional phrase.
In your example about the commas, your grammar is not correct (you've said 'is' twice) and I've no idea what your sentence means. How do you see someone off with a comma?
Best wishes, Clive