8．A．They are going to London tomorrow morning． B．They started early in the morning to go to London． C．They are thinking about going to London as early as possible．
3．A．Tom will send me a letter when he arrives in Beijing． B．Tom will hear from me as soon as he arrives in Beijing． C．Tom won't write to me even if he arrives in Beijing．
20．A．Many people are worried about air pollution in our city： B．Many people in our city are worried about air pollution． C．Many people in our city worry about air pollution．
