A．The nation has raised alert status to the highest level and thousands of people have moved to safety.

B．The eruption of Mount Merapi has been the worst in Indonesia over the past two decades.

C．All residents in the region ten kilometers from the base of the mountain have evacuated.

D．The eruption process was a sudden burst and has caused extensive damage and heavy casualty.

使用大尺寸钻铤有助于防止井斜。