下列运算正确的是
A.a3a4=a12
B.a6÷a3=a2
C.2a﹣3a=﹣a
D.(a﹣2)2=a2﹣4
答案:C
________ away from school for two weeks, I have quite a few lessons to catch up with.
A.Having been
B.To be
C.Been
D.Being
(10 分)(1)明矾的组成为 ,明矾的用途 ,其在水中的电离方程式是 。
(2)除去Na2CO3粉末中混入的NaHCO3杂质用 方法,化学方程式为 。