试比较: 1. This is the place where I lived ten years ago . The school , where I once studied , was built thirty years ago. 2. He is a man who I can ask for help. His father , who works in Beijing, came back yesterday.
Leading - in
限制性定语从句和先行词关系密切,如果去掉从句,剩余部分意义不完整;非限制性定语从句只是先行词的附加说明,如果去掉从句,意义仍然完整。