1．Dust and dirt soon a____________ if a house is not cleaned regularly.
2．It would be u____________ that such an honest fellow should have betrayed his friends.
3．Despair is a s____________ of weakness.
4．He told a rather rude joke，and everyone looked e____________.
5．The teacher’s explanation c____________ the puzzling problem.
6．We have several questions ____________(关于)the report.
7．This button is for ____________(调整)the volume.
8．The equipment must be bought from a supplier ____________(认可)by the company.
