请改写下列句子: prefix="o" ns="urn:schemas-microsoft-com:office:office" ?xml:namespace> 1.An unknown object was flying across the sky just when he looked up. ___________ when he looked up ________ an unknown object was flying across the sky. 2. His parents’ health is falling down day by day. He is worried about it very much. _____________him most ___________ his parents’ health is falling down day by day. 3. The plan was a complete failure in the end. The plane ________________ a complete failure. 4. All of us know that taking part in social activities is beneficial to broaden our view and strengthen our sense of cooperation. _________________________ , we can broaden our view and strengthen our sense of cooperation by taking part in more social activities. 5. As there was a big rock getting in the way, all the passing cars and trucks couldn’t get through. ____________a big rock _________ in the way, all the passing cars and trucks could not move on. 6. Last year, we visited that magnificent palace. Its beauty can’t be described in words. Last year, we ___________________ that magnificent palace, _________________________. 7. He stood there for quite a few minutes and didn’t know what to do next. He stood there for quite a while, __________________ what to do next at all. 8. He goes to that club for a swimming training every Saturday. It has become a regular rule. He___________________________ go to that club for his swimming training every Saturday.