SAT English Practice Question

The passage is about the history of the internet, and the author explains how the internet has changed over time. The author also explains how the internet has impacted society and culture. The author notes that the early internet was a very different place than it is today, but it is clear that the author believes that the internet will continue to evolve and change in the future. What is the most likely reason why the author uses a comma to separate the two clauses "but it is clear...evolve and change"?

1. A.separate two independent clauses.
2. B.separate two dependent clauses.
3. C.separate an introductory phrase from the main clause.
4. D.separate a nonessential clause from the main clause.