用“介词+关系代词”完成句子

1.I have five English dictionaries__among which____Longman Dictionary is the best.
2.He built a telescope __in which____he could study the skies.
3.I have come to explain the reason __for which____I was absent from the meeting.
4.The park __to which ____he took us was very beautiful.
5.Yesterday we visited the West Lake __of which ____Hangzhou is famous.
6.The naughty boy made a hole in the wall __on which____he could see what was happening outside.