The correct answer is D. No error.
The sentence is grammatically correct. The word “show” is a linking verb, and the phrase “a mind fully awake in the possibilities of social reconstruction” is a predicate nominative that describes the subject
of the sentence, “Locke’s treatises on government toleration and education.”The sentence could be improved by adding some more detail. For example, we could say “Locke’s treatises on government toleration and education show a mind fully awake in the possibilities of social reconstruction, arguing that education is the key to a free and just society.”