He started to learn English in 1990 and in the years ________ he kept on using it in his work.
The opening ceremony is to be held in the lecture hall this afternoon, _____ can seat 400 people.
It is reported that no problems have been discovered in milk products such as Yili, Sanlu and Mengniu, ________ proves newly-produced liquid milk safe.
Was __ at the air battle on June 8,1994, ____ was led by Captain Johnson ___ Peter lost his life?
Could it be in the restaurant ________ you had dinner with me yesterday ________ you lost your handbag?
He said that the key _____ to open the door had been lost.