– I wonder how much you charge for your services. -- The first two are free________the third costs $30.
Another type of pollution, ______ thermal pollution (热污染), is caused by fuel-burning.
They had great difficulty ____ the people ____ in the fire.
It was midnight _____we reached the station.
When he turned professional at the age of 11, Mike _____ to become a world champion by his coach and parents.
In some countries where there is not enough coal, water is used to ____ electricity.