题目内容：
根据下列材料，回答题：It was December 25. Marie, a 13 -year- old Australian girl, was happy. It was Christmas, and Marie' s mother was making a special cake. She put four small coins into the cake, and then she baked (烤) it. The four coins were for good luck. After dinner Marie and her family ate the cake. They found three coins in the cake and put them. on the table. Where was the fourth coin It was missing, but Marie's mother didn't notice.
After Christmas Marie got sick. She coughed, and she couldn't speak. After six weeks she felt better, but she' still couldn't speak. Marie' s parents took her to hospital. Doctors at the hospital looked her over, and then said, "We are sorry, but we can't help her. "For 12 years Marie didn't speak. She grew up, she got a job, and she got married. But she never spoke. One day, when Marie was 25 years old, she got a sore throat (嗓子疼) at work. She began to cough. She coughed up something small and black. What was it Marie didn't know. She took it to the hospital. A doctor at the hospital said, "This is a coin!" The doctor told Marie, "I think you can speak again. " Marie went to a special doctor, and soon she could talk.
What did Marie's mother make on Christmas
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