1.My hotel room overlooked a courtyard,in which there was a fountain and several trees.（定语从句）
2.Uncle Charles looked everywhere for his glasses, he could not find them though.(放在此处比较口语化,置于句首也可以)
3.During Christmas,there was so much extra work at the post office that a great number of students were employed to help.(so...that...意为：如此...以至于）which 的后面为什么要加there啊？然后那个第一句能不能这样改：My hotel room in which overlooked a courtyard as a fountain and has several trees.非常感谢！in which引导了后面的定语从句。there be 表示存在的“有”啊，总不能用have 吧。不能那样改，语法上不通。这句话的意思是：我住的旅店房间能看到一个院子，那里有一座喷泉和几株树。