用化学用语填空:
(1)氦气____ . (2)五个碳酸根离子____ .
(3)两个氯原子____ . (4)最简单的有机物____ .
一Yes, ____(I ,already ,finish)
化简:(2a+1)(2a﹣1)﹣4a(a﹣1)
She practices ____ (play) the piano every day.