your father is at a meeting your father ___ ____a meeting

your father is at a meeting your father ___ ____a meeting your father is at a meeting为什么要加at和用ing形式啊 your father is at here ---Where's your father?---He ----Beijing for a meeting.He 'l Is your father a doctor? Where is your father?--At Mr Green' Is your father good at drawing? my father is your uncle .your frandfather is my ___?A.uncle is your father in H( ) is your father? where is your father? What is your father?