The subordinate clause starts with a subordinating conjunction and contains the entire dependent clause. Because is a subordinate conjunction and makes the clause dependent because you need to know what's next. Hopefully answer choice D has all the right pieces. The main clause is "it is revolutionizing medical research". This clause is a complete idea by itself and is not a subordinate clause.
Conjunctions are joining words that link together parts of a sentence. The three main coordinating conjunctions are 'and', 'but' and 'or'. They can be used to join together two clauses in a sentence
