The correct option is C Has been elected
The subject of the sentence is “prime minister” This suggests that either the subject is doing the action or some action is being done on them. The adjective “new” suggests that the prime minister has recently come through election. So, the action of electing has been done on the subject, i.e. the prime minister. Our presumption is confirmed by the fact that all the answer options have the verb “elect.” Hence, the sentence is in passive voice as the action would be done on the subject. Also, we can understand that the action has already happened as the prime minister is “new” and has already got this position. So, the sentence is in present perfect tense. The present perfect is made using the auxiliary verb 'have/ has' plus the 'past participle' of the main verb. Also, in case of passive voice, “been” is used with “have.” The option that incorporates all these elements is the correct answer. Hence, Option B is the correct answer as it uses “has” as well as “been” indicating the passive voice of the sentence and past participle of the verb “elect,” i.e. “elected” as required by the present perfect tense of the sentence. Also, note that “prime minister” is a singular verb and so helping verb “has,” not “have,” would be used with it.
Option A cannot be used as “been” indicating the passive voice of the sentence is missing from the option.
Option C cannot be used as the verb “have” cannot be used with singular subject of the sentence.
Option D cannot be used as the verbs indicating the passive voice and present perfect tense of the sentence are missing.