The correct option is D No error
Let’s examine the sentence: “He has just been appointed ambassador to an important country for a five-year term.” The sentence talks about him being appointed as ambassador. The action has just completed and so the sentence requires the verbs of present perfect tense. The present perfect is made using the auxiliary verb 'have/ has' plus the 'past participle' of the main verb. The sentence uses helping verb 'has' would be used as the subject is singular and 'been' is used as the sentence is in passive voice and action is being done upon the subject, ‘he.’ So the sentence uses correct verbs and also the rest of the sentence is correct. Hence, the sentence does not have any error. So, Option D is the correct answer.