C is incorrect, because the author does not condemn appeals to tradition altogether. Rather, the author offers a different interpretation of the same tradition.
"If any policy could be justified by those appeals to tradition, it would be the policy of determining the length of the school year according to the needs of the economy." This tells me that the author is not entirely opposed to appeals to tradition. Also, the author never suggests that there is some secret issue that is being concealed by tradition. There just isn't any support for C in this passage.
E makes a reference to the author's alternative interpretation of US history, which is why it is the correct answer.
