Unlike the fossil fuels of today, biofuels are renewable sources, which mean that they will not ____ easily.
Don't leave the water while you brush your teeth.
We arrive at six. But I'm sorry we are late.
Only to use this reading room. Students have another room on the second floor.
The police will have to the room for fingerprints.
once before, after your class I got my visa(签证). So thank you again.