In the question given below, a part of the sentence is in bold and italicised. Below are given alternatives to the bold and italicised part which may improve the sentence. Choose the correct alternative. In case no improvement is needed, choose option 'D' as the answer.
His father won't be able to leave for Varnasi until they have arrived.
until they arrive
until they will have arrived
until they will arrive
No improvement
Correct answer is A
No explanation has been provided for this answer.