mbanit wrote:Which option best express the idea.

1) Of the top-grossing films of the 1980s, only a few, which complied with MPAA standards, could be seen by children without parental guidance.


2) Of the top-grossing films of the 1980s, only a few that complied with MPAA standards could be seen by children without parental guidance.

The answer depends on the context of the sentence:

An essential modifier is one that is important to understand the meaning of the sentence.

Example:

I live in city that is the capital of India.

==> Here, the city has been defined by the "that clause", which is essential to understand in which city I am living.

Non-essential modifier:

A non-essential modifier is one that is not essential to understand the meaning of the sentence.

Example:

I live in New Delhi, which is the capital of India.

==> Which is the capital of India" is a non-essential part of this sentence. Without this "which" clause one can easily trace that I live in a city that is the capital of India.


Now, come to your sentence:

1) Of the top-grossing films of the 1980s, only a few, which complied with MPAA standards, could be seen by children without parental guidance.

===> From this sentence any one is supposed to know about those few films. It is supposed that all know about those few films and that all know those few films have complied with the MPAA standards.

Therefore, if you mean that all already know about those few films and that those few films have complied with the MPAA standards, only then you can use the "which clause" as you have used.

AND ABOUT THE SECOND ONE:

2) Of the top-grossing films of the 1980s, only a few that complied with MPAA standards could be seen by children without parental guidance

---> So, the fact, the few films have complied with MPAA standards, is not known to all; therefore, it is required to use the essential that clause.

Now, it is your deal which one would you like to use.

HTH.