________ I had walked for six hours, I was tired out. 

_______ is well known is ________ the Diaoyu Islands have been part of China since ancient times.

 Although he knew little about the large amount of work done in the field , he succeeded ____other more well-informed experimenters failed.

David is such a good boy ________all the teachers like him.

Each time ________ they met, they would talk long hours together.