In an experiment of Cr(VI) removal by an ion-exchange technique, there were 5 levels of factor pH, pH=3.0, 5.0, 7.0, 9.0, 11.0. Under each pH level, the Cr(VI) removal treatment was triplicate, that is to say, conducted 3 times. Which below may be the correct expression about this experiment?
A.
Mean square (MS) can be expressed as the sum of squares divided by the degree of freedom.
B.
The total degree of freedom is 14.
C.
The degree of freedom among groups is 4.
D.
The degree of freedom of error is 10.