Mrs Green is going to have a birthday party (生日宴会) for Mary. Mary' is her daughter(女儿) Mary' is going to be thirteen years old. A lot of friends of Mary's are going to tile party. They are all girls and there are twenty of them. Mrs Green is getting ready for the party. Mrs Wbge is belping her. 'That's a pretty(精致的)cake. ' Mrs White says to Mrs Green. 'Thank you. ' Mrs Green is going shopping now. She's buying sonlg frug for die party. She buys a lot of oranges. apples and bananas. Then she goes home. It's three o'clock in the afternoon. Everything is ready. Now tile first girl is arriving (到达). The party is going to start in early ndnules. Mary is going to be ______ years old.