Answer:
Adjective clause
Step-by-step 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 (who, whom, whose, that, or which) or a relative adverb (when, where, or why).
The sentence "A tree surgeon removed the branches that were dead," contains an adjective clause ("that were dead") because this clause adds further detail to or describes the noun "the branches."