The passage starts off by telling us that Newton's Principia could initially only be understood by a few people. However, a basic understanding of Newton's ideas eventually spread throughout the world.
The author tells us that this demonstrates that the communication barriers between scientists and the public are not impermeable.
Therefore, the author concludes that recent scientific research may also eventually spread throughout the world.
The claim that most recent scientific research can currently only be understood by a few people links the author's anecdote about Newton to the passage's conclusion. This is restated by answer choice (D), making it the correct answer.
Hope this helps! Please let us know if you have any further questions.