A:购买一张福利彩票,中特等奖
B:在一个标准大气压下,加热水到100℃,沸腾
C:任意三角形的内角和为180°
D:在一个仅装着白球和黑球的袋中摸出红球
A. Take turns.
B. Keep your desk clean.
C. Work quietly.
D. Talk quietly.
E. Keep to the right.
计算2a2-a2的结果是( )