A: 0.85 ´ 105
B:8.5 ´ 104
C:85 ´ 10-3
D:8.5 ´ 10-4
--- When is your birthday? --- It's _____ September.
用化学符号填空:
2个氮原子____ ;2个氧分子 ____ ;2个镁离子____ ;+2价的钙元素 ____ .
—____
拼一拼,写一写。
y+ ou= ____
y+ao = ____