Your post is a bit confusing, but I take it you are simply looking for an agent to specifically market the FILM rights to the book you have already had published, correct?
In which case you are approaching this agent (or any other) in order to ask them to represent and market the rights for film or television. Those rights are generally optioned first.
Or have I misunderstood you? Do you have a script that you have already written, based on your book - and you would like an agent to rep THAT?
This is correct, and I'm afraid that Nike isn't quite right in respect to the whole option/sale issue.
An option is not a "rental" of the rights.
That would be the equivalent of a "license" -- which is what a publisher gets. You, as the copyright holder, license a publisher to publish your work (say a novel) in a given market for a limited period. It's almost the equivalent of a rental -- a lease. And when the lease "expires" -- you get the rights back and if they want to re-publish it, unless there's some extension built into the original agreement, they have to renegotiate, or you can go somewhere else.
Nothing whatever to do with movie rights, which are, as a rule, a one-time only and absolute sale.
When someone wants to buy the rights to your material (and this applies to a screenplay as well as a novel) they will make you an offer to buy.
This isn't necessarily a full contract, but it will lay out all of the key terms. It may be called a "short form agreement" -- it has various names, but basically -- it's a contract minus the more detailed boiler plate.
But as a rule, since most of the time the money to make these things -- books or screenplays, isn't there up front -- they don't want to buy it up front.
That's where the "option" comes in.
They need to get the material tied up -- they need a guarantee that they'll be able to buy it on terms that both sides have agreed to -- but they don't actually want to have to buy it unless they know that someone is going to be willing to make the movie.
Otherwise, what would be the point? They'd have spent a lot of money on the rights to something that will ultimately prove to be worthless.
So the include, in that short form contract the terms of an "option."
That means, quite simply that they they haven't bought your script yet, but they have the exclusive *option* to buy it, at the terms that you've agreed to, within a period of time that you've mutually agreed to (a year or eighteen months, as a rule) for an amount of money up front, that you've agreed to.
And usually, there's a built-in extension, for an additional payment.
That's what an "option" is -- you're giving someone the exclusive option to buy the rights to your material. During that period, you can't sell it or give an option to anybody else, for any amount of money.
It is theirs to buy, at the price agreed to, for as long as the option lasts. If they manage to get the movie "set up" -- that is, they get the financing in place, or at least feel that the project has moved far enough along to justify acquiring the underlying material, then they will "exercise the option" -- that is, they will pay you the purchase price, minus the cost of the initial option (that's usually how these contracts are structured).
At that point, they will own the rights -- either the movie rights to the literary work, or in the case of a screenplay, the rights to the screenplay in total.
Now, it is possible -- and sometimes people have done it -- to get a "non-exclusive" option -- to tell somebody (generally someone who isn't paying you any money up front) -- yeah, if you can get this set up, you can buy it from me at these specified terms -- but you're not exclusive. If I can get somebody else to pay me more, the deal is off, because you're not paying me anything.
But not many companies will agree to that because, from their perspective, they're investing a lot of time in trying to get your project set up -- and they will always consider their time trying getting a project set up to be more valuable than the time it took you to write the script, for which they will generally try to give you as little up front as possible.
I hope that clarifies what people talk about when they refer to something being "optioned."
NMS