Explanation
Correct answer: C.
Choice C is the best answer. The word "earning" is being used to introduce an additional modifying phrase, which describes how Fairuz’s repertoire lent her cross-generational appeal. When a verb ends in -ing and doesn’t have a helper verb like "is" before it, it can be used to modify a noun or verb. This is appropriate here.
Why the other choices are wrong
Choice A
Choice A is incorrect. The underlined verb is being used to introduce additional descriptive information, which is set off from the rest of the sentence by a comma. Because there is no subject here, a finite form of the verb (like "earned") creates an error. We need another form of the verb that doesn’t require a subject and can introduce descriptive information.
Choice B
Choice B is incorrect. The underlined verb is being used to introduce additional descriptive information, which is set off from the rest of the sentence by a comma. Because there is no subject here, a finite form of the verb (like "had earned") creates an error. We need another form of the verb that doesn’t require a subject and can introduce descriptive information.
Choice D
Choice D is incorrect. The underlined verb is being used to introduce additional descriptive information, which is set off from the rest of the sentence by a comma. Because there is no subject here, a finite form of the verb (like "earn") creates an error. We need another form of the verb that doesn’t require a subject and can introduce descriptive information.