Wind power is an ancient source of energy ______ we may return in the near future.
Their class is __ a camera, a TV and a computer.
Every time I went to visit Mount Tai, it __ me with its nature beauty.
All the staff in our company are considering ___ to the city center for the fashion show.
Only by shouting at the top of his voice, ___.
The hill ____ is covered with tress is called Huang Hill.