The correct option is A is going to be allowed
Here, 'is going to be allowed' in Present Continuous Tense is correct as it implies
an action going on at the time of speaking.
'Will allow' in future simple is incorrect as it indicates
an action, condition or circumstance which has not taken place as yet.
'Will be allowing' in future continuous is incorrect as it indicates
what will be going on in the near future.
'Has been allowed' in present perfect continuous is incorrect
because it is used to indicate an action that started at some point in the past
and may or may not be complete.