The correct option is A and
From the given options, we can compare the function of the conjunctions to eliminate the inappropriate answers. The option 'while' is used to express time or contrast, thus it does not fit correctly in this sentence. Option 'until' is also used to denote time. So this is also incorrect. Option 'as' is used to connect the result of something with its reason. So 'as' is not appropriate for the given sentence. 'And' is a coordinating conjunction that is used to join two or more clauses of equal importance or rank. Thus, option A.'and' is the right answer. So the completed question thus becomes :John welcomed his guests and offered them drinks.