Explanation: In English grammar, subject-verb agreement is a fundamental principle that ensures the subject and verb in a sentence agree in number and person. This means that if the subject is singular, the verb must also be singular, and if the subject is plural, the verb must be plural. This rule applies to all persons (first, second, and third) and all tenses.
For third person singular subjects (he, she, it, singular nouns), the verb must end in -s or -es in the present tense. For example, "He sings," "She dances," "It runs," and "My mom sings." The verb "sing" in its base form is used for first and second person singular and all plural subjects, such as "I sing," "You sing," "We sing," and "They sing."
In the given sentence, "My mom sings beautifully," the subject "mom" is a third person singular noun. Therefore, the verb must be in its third person singular form, which is "sings." The sentence "My mom sings beautifully" is grammatically correct because the subject and verb agree in number and person.
Option A, "Sing," is incorrect because it is the base form of the verb and does not agree with the third person singular subject "mom." Option C, "Is sing," is incorrect because "is sing" is not a valid construction in English. The correct form would be "is singing" if the sentence were in the present continuous tense, but the sentence requires the simple present tense, which is "sings." Option D, "None of the above," is incorrect because one of the other options (B) is correct.
Understanding subject-verb agreement is crucial for constructing grammatically correct sentences in English. It is a concept that is frequently tested in various competitive examinations, including UPSC, SSC, Bank PO, and CLAT, where candidates are expected to demonstrate a strong grasp of English grammar.