单项选择题 锥面与顶面的夹角称为气门锥角。

单项选择题 《煤矿安全质量标准化标准》规定，防治水应坚持“有疑必深”，凡不清楚或有怀疑的地段，都必须安排探放水井有防探水钻孔设计及( )。

单项选择题 (句子释义)The wretched boy never set foot upon a football field without scoring a goal.A. Each time this boy played football, he was sure to get the ball into the goal.B. This unfortunate boy never played football, as he couldnt score a goal.C. This boy was unhappy because he didnt kick the ball into the goal.D. If this boy didnt score a goal he would feel wretched.