In the following questions, in the given sentences, a part of the sentence is underlined. Beneath each sentence, four different ways of phrasing the underlined part are indicated. Choose the best alternative.

His father won't be able to leave for Varanasi until they have arrived .

A. until they arrive

B. until they will arrive

C. until they will have arrived

D. No improvement

Please do not use chat terms. Example: avoid using "grt" instead of "great".