kashefian wrote:Declining revenues resulting from a decrease in business travel, a source of income without which most commercial airlines could not survive, are going to force many commercial airlines to increase prices and decrease services in the coming months.
(A) a source of income without which most commercial airlines could not survive, are
(B) a source of income without which most commercial airlines could not survive, is
(C) and most commercial airlines use it as a source of income to survive with, are
(D) which is a source of income which is needed by most commercial airlines who could not survive without it, are
(E) which most commercial airlines use as a source of income without which they are unable to survive, is

What is the OA?

Do you consider the subject plural or singular?

IMO A
Declining revenues is the subject so plural i guess

Subject is declining revenues i.e. plural. Only A makes sense

Revenues is the subject. All other phrases around it are modifiers.

Revenue is singular.
Revenues is plural.

To match the plural subject, the corresponding verb has to be plural.

A is right.

Revenues is the subject. All other phrases around it are modifiers.

Revenue is singular.
Revenues is plural.

To match the plural subject, the corresponding verb has to be plural.

Referring to Manhattan GMAT sentence correction, chapter 3, "Subject phrases and clauses: Always singular" I would argue that "Revenues" is not the subject here. "Declining revenues" is the subject which is a clause. We say: Declining revenues is going to force many airlines to.... we do not say declining revenues are going to force ....

As the Manhattan GMAT sentence correction provides us with a similar example: Having good friends is a wonderful thing (not are a wonderful thing)

What do u think?

IMO its A

Declining revenues resulting from a decrease in business travel, a source of income without which most commercial airlines could not survive, are going to force many commercial airlines to increase prices and decrease services in the coming months.
(A) a source of income without which most commercial airlines could not survive, are
(B) a source of income without which most commercial airlines could not survive, is
(C) and most commercial airlines use it as a source of income to survive with, are
(D) which is a source of income which is needed by most commercial airlines who could not survive without it, are
(E) which most commercial airlines use as a source of income without which they are unable to survive, is

Declining revenues, so it has to be are and not is. With this we can strike out B and E

C introduces and which is not needed and so out and D has needed by most commercial airlines (passive tone) and moreso its too wordy.

So IMO it is A.

Please read my last comment. Any idea about Subject Clauses?

kashefian wrote:

Revenues is the subject. All other phrases around it are modifiers.

Revenue is singular.
Revenues is plural.

To match the plural subject, the corresponding verb has to be plural.

Referring to Manhattan GMAT sentence correction, chapter 3, "Subject phrases and clauses: Always singular" I would argue that "Revenues" is not the subject here. "Declining revenues" is the subject which is a clause. We say: Declining revenues is going to force many airlines to.... we do not say declining revenues are going to force ....

As the Manhattan GMAT sentence correction provides us with a similar example: Having good friends is a wonderful thing (not are a wonderful thing)

What do u think?

Here Declining revenues means, there are revenues(plural) and those are declining. Still the subject is Revenues here where declining is just an adjective.

Having good friends is a wonderful thing. Here having is the action of a person but not an adjective. Moreover, subject is the clause not friend; so it is correct.

My playing friends are a wonderful thing to me. Here friends are subject and playing is just an adjective to friends.

kashefian wrote:
Referring to Manhattan GMAT sentence correction, chapter 3, "Subject phrases and clauses: Always singular" I would argue that "Revenues" is not the subject here. "Declining revenues" is the subject which is a clause. We say: Declining revenues is going to force many airlines to.... we do not say declining revenues are going to force ....

Whoa! Hold on!

First, declining revenues is not a clause. A clause, by definition, needs a subject and a verb. We do not have a verb here.

Now consider the following sentence,
Declining revenues are forcing airlines to raise prices.

Let us understand the structure of the sentence -
revenues - Subject
Declining - Modifier modifying the subject.
are forcing - Verb
airlines - Indirect object
to raise prices - infinitive phrase acting as a direct object.

Here the subject is still revenues. Declining is just a modifier. According to subject verb agreement, the verb must correspond to the subject. Modifier has no effect on the number of the subject. Since the subject is revenues (pl), verb has to be are (pl)

Consider these parallel sentences -

1. Barking dogs seldom bite - Here the subject is dogs (pl). So the verb is bite (pl).

2. Barking dog seldom bites - Here the subject is dog (sing). So the verb is bites (sing).

Note that the modifier has no effect on the verb. The verb must match only with the subject.

kashefian wrote:
As the Manhattan GMAT sentence correction provides us with a similar example: Having good friends is a wonderful thing (not are a wonderful thing)

Let us analyze this example -

Having good friends is a wonderful thing

What is the subject of the sentence?
Something (a noun) is a wonderful thing.

something is the subject of the sentence.
is is the verb.
a wonderful thing is the subject complement.

In this sentence, this something is having good friends. So the phrase having good friends is the subject of the given sentence. It is a noun phrase because it acts as a noun.

According to the rule quoted by you, a noun phrase is always singular in number. That is why we need a singular verb is in this sentence.

P.S. Note that having good friends is a phrase and not a clause.

Thank you niksworth. Totally understand the topics..