which引导的定语从句例句：A shop should keep a stock of those goods which sell best（商店应存有最畅销的货物）；This is a reason which we must not forget（这是我们不能忘记的一个原因）。

which引导的定语从句例句：This is the family which is planning to move to the city（这是要搬进城里的一家）；When deep in thought，which he often was, he would forget all around him（他常常陷入沉思，这时他就会忘掉周围的一切）。