用＂介词+关系代词＂完成句子
①Do you still remember the days __________________________we worked together?
你还记得我们在一起工作的那些日子吗？
②The social problem __________________________ the two sides are debating with each other is a very serious one.
双方正在展开辩论的社会问题是很严重的一个。
③Water is of great importance, __________________________ people can not live.
水是很重要的，没有它人们就无法生存。
④This is the book __________________________ you have talked to me.
这是你曾经给我谈起的那本书。
⑤This is the book on the cover __________________________ there is a map of China.
这是封面上有张中国地图的那本书。