Fix the adverb error (if one exists).​The ​basketball ​player ​can ​reach ​more high ​than ​Mr. ​Filch ​can.

The sentence contains an adverb error. The word "high" should be replaced with "highly" to appropriately modify the verb "reach."

Here’s the corrected sentence:

Corrected Sentence: "The basketball player can reach more highly than Mr. Filch can."

Explanation:

In this context, "reach" is a verb, and when describing how one can reach something, we use the adverb form. The comparative form of the adverb "highly" is used to indicate that the basketball player reaches to a greater degree or extent compared to Mr. Filch.

This change enhances clarity and grammatical correctness, ensuring that the adverb accurately modifies the action of reaching rather than describing a noun, which would require an adjective. Adverbs are crucial in providing context to actions, thus refining the overall quality of the sentence.