Hey All,
Seems like there were a couple of follow-up questions here, which I'm happy to help on.
#1: The first asked how to use a relative pronoun to only refer to one item in a list. As far as I know, there is no way to do this without a bit of ambiguity. Ambiguity is one of those issues that isn't NECESSARILY wrong on the GMAT, but most often is. As an example:
The table and chairs, which I bought at Ikea, are great.
Do we know whether I bought JUST the chairs, or the table and chairs, at Ikea? No. Ambiguous, but probably okay.
The house and the birds, which can't even fly, will be going to my ex-wife in the divorce.
In this case, the which clearly refers to birds, but it's through logical context, not grammar, that we get it. Thus this would still be considered ambiguous, but probably okay (hopefully there's be an answer choice that offered a better solution). Either way, the verb "will" in this example, like the word "are" in the previous example, must be the verbs that go with the compound subject (table and chairs OR house and birds), because the word AND always creates a compound subject.
#2: As for the other question, this involves the use of ARTICLES. Articles are words like "a", "the" and "an". The rules for these are so hardwired into our heads that we sometimes forget they exist. Basically, you have to use articles in certain singular cases:
I have a headache NOT I have headache.
I have the house NOT I have house.
But generally with plural nouns, the article changes the meaning.
I have dogs (general) OR I have the dogs. (specific)
This example has a singular noun (life-style). This requires an article in front of it.
I have a lifestyle NOT I have lifestyle.
This makes answer choice A incorrect anyway. However, articles DO NOT define the number of the noun itself. The fact that there is an "a" before "life-style" is not what makes "life-style" singular. You simply have to put an "a" in front of a singular noun in this case.
Feel free to continue asking follow up questions, but hopefully that made sense. : )
-tommy