ok, slightly mixed up about these.
For a few questions, OG says that you must use an "-ing modifier".
Here is my understanding....
words like that, who, and which are adjective modifiers that modify the noun before it.
words like when, where, and any -ing form of a verb are adverbial modifiers, and modify a verb.
but in OG, they sometimes have -ing modifiers modifying the noun (rather than the verb) right before it.
I did it all for the Starwood points.