Prepositional Phrases Clarified

After going through several sources, I made some points that I would like to share with everyone.
First of all, before even advancing, I shall ask a question.
His collections of music IS/ARE good.
What is correct here?

Before advancing further, the keything to understand is:

1)As an adverb, a prepositional phrase will answer questions such as How? When? or Where?
i)Freddy is stiff from yesterday's long football practice.

How did Freddy get stiff? From yesterday's long football practice!

ii)Before class, Josh begged his friends for a pencil.

When did Josh do his begging? Before class!

2)As an adjective, the prepositional phrase will answer the question Which one?

Read these examples:

1)The book on the bathroom floor is swollen from shower steam.

Which book? The one on the bathroom floor!

2)The sweet potatoes in the vegetable bin are green with mold.

Which sweet potatoes? The ones forgotten in the vegetable bin!

Now here is the trick.

Subject never resides in prepositional phrase, EXCEPT when quantity is expressed.

In the clauses where quantity words are used, WHICH or other relative pronouns will NOT JUMP otherwise it will have to jump.Consider an example:
The box of nails, which is black in color, is kept on the table.
Here the prepositional phrase is "of nails". But it can't be the subject because we have not used any quantity word here.
Now consider this:
Some of the stones, which were thrown by Sam in Thames, were round in shape.
Here the prepositional phrase is "of the stones" but since SOME is a quantity word here, hence subject is "stones" not "some of the stones".

More example to clear the doubt. (The subject is green in color.)
1) Seven of the eleven medals, which were all gold, were won by Jamaican sprinters.
2) Most of the bananas have been bought from the nearby market.
3) A number of supporters of the the campaign have extended their support for Democratic Party.
4) THE number of birds migrating to the Marina Beach is increasing year by year.

So remember one thing, if any quantity word precedes the prepositional phrase, then your subject will reside in the prepositional phrase.
By the way, the answer to the question at the top is "ARE".

Source: MGMAT, e-GMAT and Jamboree
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