_____is a website which uploads content in a video format. It houses a range of interesting videos that appeal to people of all generations.
A. Facebook
B. Twitter
C. YouTube
D. Amazon
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Which of the following isthe trend of media development?
All of them are building a multi-media platform.
B. The competition of media becomes more and more complex.
C. Merger and takeover will continue to occur.
D. All above.
与水平线垂直的直线一定是（ ）。
A. 水平线
B. 侧平线
C. 正垂线
D. 铅垂线
直线的投影变换中，（ ）变换为投影面垂直线时，新投影轴的设立原则是新投影轴垂直反映直线实长的投影。
A. 平行线
B. 倾斜线
C. 垂直线
D. 一般位置直线
直线的投影变换中，一般位置直线变换为投影面平行线时，新投影轴的设立原则是新投影轴（ ）直线的投影。
A. 垂直于
B. 平行于
C. 相交于
D. 倾斜于
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