I often help mother__________ housework after school.
A:do
B:doing
C:to doing
D:does
c(CH3COO﹣)+c(CH3COOH)=____mol/L
c(H+)____c(CH3COO﹣)﹣c(CH3COOH)+2c(OH﹣) (填“>”、“<”或“=”)
对下列观点或现象的解释,正确的是( )