下列四种水轮机属于反击式水轮机的是（）
A.击式双击式
B.流式贯流式
C.流式水斗式
D.流式斜击式
参考答案：B
The accident that happened at an oil field _____ the southeast coast of the USA has caused great damage
to the environment.[ ]
A. away
B. from
C. beyond
D. off
有焰燃烧必须具备四个必要条件，即可燃物、助燃物、引火源和链锁反应。
