Mr. Hall understands that _______ math has always been easy for him, it is not easy for the students. 

Do you know the man _______? 

 —I can never forget the days       we spent together in the summer camp.—Well, especially the day       it suddenly began to rain in the middle of the night.

I didn't know _____ you were getting on well with your work. 

---- Is that the small town you often talk about?----- Yes, just the one______ I used to work for years.