Answer:
The sentence that contains a gerund phrase is:
A. Practicing the piano daily has helped Maria master Beethoven's "Moonlight Sonata."
Step-by-step explanation:
A gerund is a noun created by adding -ing to a verb root. A gerund phrase, in its turn, has a gerund and any modifiers or objects related to it. A gerund phrase functions as a noun, which means it can be the subject, the object, or the predicate nominative of a sentence.
In the sentence "Practicing the piano daily has helped Maria master Beethoven's 'Moonlight Sonata'," the gerund phrase is "practicing the piano," in which the gerund is "practicing". We know this phrase functions as a noun but, to determine its function in the sentence, all we have to do is ask the verb a simple question: What has helped Maria? Practicing the piano daily has helped Maria. Therefore, we have a gerund phrase that is the subject of this sentence.