He tried his best to solve the problem, _______ difficult it was.
My father walked _____ in the room, looking as if he was thinking over something.
His proposals were _____ with cheers.
I have a great ____ and admiration for my former English teacher.
To be well-informed, we should be _____ communicationeach otherwhat happens to us.
What shall we use for power when all the oil in the world has _________?