Decling 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