Today is Children's Day. It's Mary's birthday, too. Her parents go to work early. Mary gets up and finds a red box on her bed. She opens it and sees a card in it. It says, "Dear Mary, here is a present for you. But please guess the riddle (谜语) first, The first letter is in the word book' but not in 'cook' The second letter is in 'thank, but not in ‘think' The third letter is in both ‘girl' and ‘egg'. It's blue. Look for the present in the study"Mary goes to the study and finds her present. She is very happy.
