Question

highlight the conjunction.
noun/pronoun verb article adjective preposition adverb conjunction
a man built a complicated sandcastle, but the waves washed the castle away.

Explanation:

Conjunctions connect clauses, phrases, or words. In the sentence, "but" links the two independent clauses: "A man built a complicated sandcastle" and "the waves washed the castle away."

Answer:

The conjunction is "but"