The thylacine, which was also called the Tasmanian tiger, was a dog-like creature unique to the island of Tasmania. (Option B)
Relative clauses describe nouns like adjectives do (that is why they are also called adjectival clauses) and can be classified into:
- Defining - Provide essential information about the head noun and are usually tied to the main clause (no using of commas here)
- Non-defining - Provide information that can be removed without affecting the noun (commas are used here)
They usually begin with a relative pronoun such as which, who, whom, whose, and that.
In this case, whe have a non-defining relative clause.