Answer:
<u>Adjective clause</u>
Explanation:
Adjective clauses are groups of words containing a subject and a verb whose function is to modify, describe or add more detail to nouns (a place, thing, person, animal); we can also identify them because they often begin with a relative pronoun (<em>who, whom, whose, that, </em>or<em> which</em>) or a relative adverb (<em>when, where, </em>or<em> why</em>).
The sentence "A tree surgeon removed the branches <u>that were dead</u>," contains an adjective clause ("<u>that were dead</u>") because this clause adds further detail to or describes the noun "the branches."