____caused the accident is still a complete mystery.
In China, you _____ vote when you are 18.
The professor could hardly find sufficient grounds _____his arguments in favor of the new theory.
Many workers were organized to clear away remained of the World Trade Center.
A survey was carried out on the death rate of those who were infected by SARS, ________were surprising.
In recent years much more emphasis has been put______ developing the students productive skills.