为保证焊接质量，一般规定CO2气体的纯度为99.5%以上，含水量、含氮量均不得超过（

从方框中选用合适的动词并用其适当时态填空。

quarrel    clean      hold      find     fly

1. David is a polite student. He never ____________ with others.
2. ---Where is Jack?
---He ____________ the floor in the classroom.
3. --- ____________ the police ____________ out who stole the money?
--- No, not yet. But they are busy doing it.
4. We ____________ a party to celebrate Christmas next Sunday, shan’t we?
5. His uncle often ____________ to Beijing in the past.