How to identify the function of a prepositional phrase ?

[gmatango]

Hi, I have a very general question rather a problem than I face quite often. I don't know how to identify whether a prepositional phrase modifies a noun or a verb.

Example:
After unveiling new iPods and iTunes software at an event, Apple CEO Steve Jobs invited singer Norah Jones on stage to perform for the assembled tech and media pundits.

The highlighted phrase in the above example can either modify Apple CEO (the noun) or invited (the verb). How to identify what it modifies ?

Similarly, even in the following one liner I can't identify whether the prepositional phrase refers to "class" or "goes".
Mary goes to gym class on Thursday evenings.

Please let me know is there a set method/strategy to identify whether a prepositional phrase is modifying a verb or a noun or it depends on case-to-case basis.

Thanks!

[tim]

The best way to figure out what a modifier is modifying is to ask a question the modifier answers. In the first sentence, I can’t really come up with a question about Steve Jobs that the first clause answers. However, the clause definitely answers the question "when did the inviting occur?" In the second sentence, "on Thursday evenings" could answer the question of when the gym class is or when the going occurs..