1.___________________(为了确保他参加会议),I called him up in advance.
　　2.The significant museum________________(据说建成于)about a hundred years ago.
　　3.There would be no life on earth ____________________ (没有地球独特的环境)。
　　4.______________________________(给游客印象最深的)was the friendliness and warmth of the local people.
　　5.They requested that ___________________________ (我借的书还回图书馆) by next Friday.

　　答案与解析：
　　1.To ensure his attendance at the meeting
　　2.is said to have been built
　　3.without its unique environment
　　but for its unique environment
　　4.What impressed the tourists most
　　5.books I borrowed (should) be returned to the library