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