【正文】
polite that students often give seats to the elderly on the bus. 2. It is impossible to finish all the homework in an hour. 3. It is dangerous for her to go swimming alone. 4. It is tough to walk a 100kilometre trail within 48 hours. 5. It is meaningful for Dr Ma to work for ORBIS. 6. It is sad that some children in poor areas cannot go to school.