Which word classes does the hard belong to?

"Hard" can belong to several word classes depending on its context:

* Adjective: Describing a quality or state. Examples: "The rock is hard.", "It's a hard problem."

* Adverb: Modifying a verb, adjective, or another adverb. Examples: "He works hard.", "The test was surprisingly hard."

* Noun: Representing a thing or concept. Examples: "The hard of the bread was burnt.", "The difficulty of the climb made it a hard." (Less common usage)

It's important to look at the sentence and the word's function within it to determine its specific word class.