A:( 13 , 23 )
B: 13 , 23 )
C:( 12 , 23 )
D: 12 , 23 )
— was the book sale in your school library last Sunday?
—Great.
欲除去氢氧化铁胶体中混有的Na+和Cl﹣,可选用的方法是( )
27÷3=____
36÷4=____