例句：S1:what's a letter box?S2:It's a box with a hole through which the postman puts the letter

例句：S1:what's a letter box?S2:It's a box with a hole through which the postman puts the letter
根据上面的形式改写下面句子 1.what's a gym?(in which) 2.what's a vacation?(during which) 3.what's a library?(from which) 4.what's a university?(at which) 5.what's a doctor?(to whom) 6.what's a studio?(at which) 7.who's Father Christmas?(from whom) 8.what's a good friend?(with whom)
急用！