He tried his best to solve the problem, _______ difficult it was.
The boy doesn’t like ______ when his mother compares him with the other children in the neighborhood.
The people in the Kiss Nightclub were trying to escape from the fire but were ______ in smoke.
I still remember ______ to the Science Museum for the first time when I was young.
As a result of the fog haze weather, nowadays many people are longing to live ______ the air is fresher.
—I thought you ______ for vacation tomorrow.—I had planned to, but I have a very important meeting to attend tomorrow.