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.
It could not be the first one because it doesn't say anything about what sports they play. it couldn't be the 3rd one because obviously they are not friends, galen was not very polite to Claire so it could not be the last one, so the answer is b) "Galen and Claire have an argument outside Galen’s locker."
