The correct option is A Anteroom
An anteroom is an antechamber, typically serving as a waiting room. For example, "He had been patiently waiting in the anteroom for an hour." Hence, Option A is correct. Among the rest of the options, lounge means a public room in a hotel, theatre, or club in which to sit and relax, lobby means a room providing a space out of which one or more other rooms or corridors lead, typically one near the entrance of a public building, pantry means a small room or cupboard in which food, crockery, and cutlery are kept. These options do not express the intended meaning, hence incorrect.