请辨别下列从句的类别： 1. How the book will sell depends on its author. 2. John said that he was leaving for London on Wednesday. 3. The fact is that he has not been seen recently. 4. The fact that he has not been seen recently disturbs everyone in his office. 5. He will talk to us about what he saw in U.S. 6. It is impossible that I go and attend the meeting. 7. What life will be like in the future is difficult to predict. 8. It is certain that things will cha
