Copernicus's astronomical system is superior to Ptolemy's and was so at the time it was proposed, even though at that...

Emil-Kunkin on October 9 at 09:02PM

The passage tells us that despite the fact the evidence fit both theories equally, one was better than the other, and tells us the better theory was simpler. We are looking to support the claim that one theory was better than the other despite the fact the evidence was equal. Since the only other info we have is that one was simpler, we need a principle along the lines that the simpler theory is better. This is a great match for d.