In the following question, some part of the sentence may have errors. Find out which part of the sentence has an error and select the appropriate option. If a sentence is free from error, select "No Error".
Tom Sawyer is one(A)/of the best kid stories(B)/that was ever written.(C)/No error(D)

In the structure "one of + plural noun + relative pronoun (that/who)", the verb following the relative pronoun agrees with the plural noun antecedent. Here, the antecedent is "stories" (plural), so the relative clause verb must be plural (were instead of was).
Therefore, the error is in part C. The correct sentence should be: "Tom Sawyer is one of the best kid stories that were ever written."