The correct answer is adjectival clause.
An adjectival clause is a dependent clause that works to describe a noun in a sentence. It is usually made of a group of words instead of one word only. All the words work together to modify the noun or pronoun.
A dependent clause contains a subject and a verb but it's not a complete sentence and it can not stand alone.
Adjectival clauses begin with a relative pronoun that connects them to the word they describe. The relative pronouns are: that, where, then, who, which, why etc.
In the clause who are compassionate, the who is the relative pronoun. The clause refers and modifies the noun appearing before in the sentence.