The correct option is C c
Let’s examine the sentence: “There has always been some form of education but there has not always been schools.” The clause after ‘but’ is wrongly using the helping verb ‘has.’ The helping verb ‘has’ is used for singular nouns. However, this clause has ‘schools’ as a plural noun and so it requires a helping verb that is used for plural nouns. So, the sentence requires ‘have’ instead of ‘has.’ Hence, the error is in Part c of the sentence. So, Option C is the correct answer.