【单选题】下面不属于曲面立体的是( )。
A. 球
B. 棱锥
C. 圆柱
【单选题】当把正六棱柱两正六边形的面放置于水平面位置,且使柱体前后左右对称,再绘制其三视图时,应先画( )。
A. 左视图
B. 主视图
C. 俯视图
According to the doctor, why did few people live to be sixty in the 19th century?
A. Because many people lived in poverty.
Because there were many road accidents.
C. Because there was no advanced medicine.
D. Because a woman had many children.
What causes the high death rate today?
A. Dangerous diseases.
B. Traffic accidents.
C. Too many children.
D. Few doctors and little medicine.
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