Relative clauses are clauses that provide more information about the sentence and isn’t necessary for the sentence to be complete.
1. “that we studied in this unit” (a good way to tell if it is relative is to see if the sentence makes sense if you take the phrase/clause out)
2. “that study prehistoric animals”
3. “who is a diver”
4. “that was discovered in Argentina”
5. “that we were learning about”
6. “who climb giant sequoias”
Another way to tell is that they relative clauses all start with a relative pronoun or adverb, such as who, whom, whose, that, which, when, where, or why. Hope that helps!