Meng Chen is a student in Beijing. He goes to the Forbidden City almost every day. He tells visitors about the clocks in the Hall of Clocks. Meng is one of around 300 volunteer tour guides in the Forbidden City. One third of them are university students. They hang around the palace like other visitors, but with red "volunteer" cards on their clothes. Meng said he loves spending time in the buildings where 24 emperors( 皇帝 ) spent their whole lives." Every brick fk) has a story to tell, "he said. But volunteer work is more than fun. Meng has to study for the job. It look him about three months to remember every detail( 细节 ) of the clocks in the clock gallery. And it can be frustrating. Often tourists turn down volunteer guides. "Too many people are in a rush to finish sightseeing. They don't have time to listen to us, " said Shi Hui. He is a university student who volunteers there. On his first day, Shi walked around for three hours until he found a man in his 50s who was happy to listen to him. It's always fun to have listeners who are interested in your talk. "Shi sad.