X线管套内绝缘油的作用是（）
A.润滑
B.防锈
C.绝缘和散热
D.防震
E.填充
参考答案：C
There is a group of stocks containing 7, 8, 9, 10, 10, 10, 11, 12, 13 and 30. Which of the following statement about the distribution is TRUE（）
A. In this distribution the median is 12.
B. This distribution’s arithmetic mean is 10 and the median is 11.
C. The distribution is skewed to the right and the mean is greater than the mode.
过水准面上任何一点所作的铅垂线，在该点处与水准面正交。( )
