Declining revenues resulting from a decrease in business travel

Hi there,
Verb-ing words are modifiers that define certain entities, depending on their placement in the sentence. Also, verb-ing words act as gerunds. Gerunds are formed by adding “ing” to any verb but they are nouns.

Now when a gerund is the subject of a sentence, then it is singular. Let’s understand this with the help of few examples:

1. Swimming is my favorite sport.
2. Listening to music works as the best stress buster for me.

In the above two sentences, “swimming” and “listening” are gerunds. They are nouns that form the subject of the sentence. Since “swimming” and “listening” are gerunds, they are singular in number and take singular verbs “is” and “works” respectively.

Now, if the sentence has two or more gerunds as subjects connected with proper conjunctions, then the verb will become plural. For example:
1. Swimming and listening to music relax me the most after a long day at work.

Now let’s take a look at the original sentence:

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.

Now here “declining” is a verb-ing word. Notice that “declining” is not a gerund here. It is modifier or an adjective that is modifying the noun “revenues”. It is showing one of the qualities of the revenues. So, technically the subject of the sentence is “revenues”. And since it has an adjective before it that cannot be left out as it shows one of its features, the subject becomes “declining revenues”. Now, since “revenues” is plural, we need plural verb. Answer choice A has the correct verb “are” that agrees in number with “revenues” or rather “declining revenues”.

Hope this helps.
Thanks.
Shraddha