Ignorance is not equal to stupidity, since you can often

78) Ignorance is not equal to stupidity, since you can often correct ignorance but the same is not true of stupidity

(A) since you can often correct ignorance but the same is not true of stupidity.
"you", shouldn't be there because the sentence didnot indicate that this is a connversation or something, and even so, its not clear whom it refering to.
(B) because it can be corrected and the other cannot
"it" is not obvious whether it is refering to ignorance or stupidity, and in turn, "ther other" is not clear who it refering to.
(C) for ignorance can often be corrected but stupidity cannot.
this is the best answer as it is clear and concise and gramatically corret
(D) because of the correctable nature of ignorance.
this ignores stupidity and awkward rephrase and wordy enough to make you think it is correct
(E) because the two differ regarding ability for correction
this doesn't show the difference between ignorance and stupidity. and it is not clear what does it mean

so the correct answer is C
hope that helps