Mark suddenly had a bad bellyache before class began this morning. His classmates immediately sent him to the People's Hospital nearby. In the hospital, the doctor gave him a medical check-up. The result of the examination showed that he was suffering from acute appendicitis and he needed an operation right away. The monitor of his class quickly called Mark's father and asked him to come to the hospital at once. After a while,Mark's father came and the operation began in no time. Several days later,Mark recovered.