启动过程中，出现阴极钢棒渗电解质，钢棒周围发红、炉帮发红等现象应（），补炉材料有（），氟化镁，壳面块等。
参考答案：抢救；氟化钙
箱子里有大小相同的3种颜色玻璃珠各若干颗，每次从中摸出3颗为一组，问至少要摸出多少组，才能保证至少有2组玻璃珠的颜色组合是一样的?
A.11
B.15
C.18
D.21
Which statement about the ARJ-21 Advanced Regional Jet is false().
A. It is the first homegrown Chinese jetliner for the 21st Century.
B. It is of medium range.
C. It should start to roll off the production line later this year.
D. None of the above.
