燃油锅炉燃烧室后墙挂焦的直接原因是（）。
A.油枪雾化不好
B.油、风混合不好
C.油枪位置不当
D.油压过高
参考答案：A
He hasn't slept at all for three days. _____ he is tired out. [ ]
A. There is no point
B. There is no need
C. It is no wonder
D. It is no way
罗伯逊易位携带者形成正常配子的概率为0。( )
