---What do you think of teaching , Bob? ---I find it fun and challenging. It is a job ___you are doing something serious but interesting
-Everyone says you are a good student. You are never late for school,are you? -_______.
_____ all the inventions have in common is ______ they have succeeded.
Last term our maths teacher set so difficult an examination problem _____ none of us worked out.
A cook will be immediately fired if he is found ______in the kitchen.
It was with great joy ______ he received the news that his lost daughter had been found.