I don't know ______.
A:where she comes from
B:how old is she
C:when was she born
代数式x-12在实数范围内有意义,则x的取值范围为( )
下列物质中:N2、H2O、Na2O2、Na2O、KOH、NaF,只含有共价键的物质是 ____;只含有离子键的物质是 ____;既含有离子键,又含有共价键的物质是 ____
下面图形是棱柱的是( )