When a subject is singular, a singular verb follows it and when it is plural, a plural verb follows it. This agreement between the subject and the verb is called the subject-verb agreement. In the sentence "The number of computer advancements" is the subject, here "the number" is singular, hence a singular verb will be used. The phrase 'a number of' is used with plural nouns, hence a plural verb would be used, whereas 'the number' is singular, it's the head of the subject, hence a singular verb will be used here. "The" plays an important role in the subject, determining the verb to be used. Since a singular verb is used here, 'is' is appropriate, it's the form of 'to be' used in sentences of the third person singular point of view. Singular verbs like 'is' end with an s whereas plural verbs don't. Hence option B is correct. Option A is incorrect as the subject is singular, and 'are' is used when the subject is plural. 'Has' is used when the subject experiences something or owns something. 'Has' is in the third person singular point of view, but is followed by a verb in the past tense, to suggest that the action has already been completed 'had increased', or in the present perfect continuous tense, 'has' is followed by 'been' as in 'has been increasing'. Here the sentence is in present tense, so 'been' would have made the option correct, otherwise, option C is incorrect. 'Have' is a plural verb, whereas we need a singular verb. Hence option D is also incorrect.