Because genetics is now progressing so rapidly.
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.
Quick question: what story are you referring to?
I believe the word that fits in the blank there is "downfall". Hope this helps you out!! :)
