Walking and running are the oldest and newest, excellent _________ exercise for all ages and fitness levels.
It is said _________ was how Chinese characters developed.
The coin was almost worthless. So it was of small ________.
She had hardly got back to the kitchen ________ the doorbell rang.
They discovered the cause of the fire accidentally. They discovered it _______.
They lost their way in the mountain and _________ made matters worse was _______ it was getting dark.