Question

理解不了它的这个连接词为什么用where 而不用which,这个that不可省略吗?.为什么.

Answer 1

a desk where he wrote letters

改为陈述句为：he wrote letters at a desk.所以是“at which” 或者是“where” ,只有which是不对的.定语从句的连接词判断一般都可以用这种方法的,改为陈述句语序判断.

that his father used to sit in

这个好像不大对,应该改为which的,that是不能与介词搭配的