In communication, a smile is usually _____ strong sign of a friendly and _____ open attitude.
At minus 130℃, a living cell can be ______ for a thousand years.
The traditional view is ______ we sleep because our brain is “programmed” to make us do so.
______ he referred to in his article was unknown to the general reader.
Small sailboats can easily turn over in the water ______ they are not managed carefully.
His movie won several awards at the film festival, ______ was beyond his wildest dream.