1. I joined the Youth Volunteers five years ago.2. I have been a member of the Youth Volunteers for five years.3. Hi Tony, you look a little tired. Yes I am. I have been cleaning the living room all day.4. Mr Smith has been writing a book. This book will probably be published next year.5. I have been telling you/told many times, dont be late!6. I have just come back from the USA. 7.8.1实 用 文 档