DNA being placed with DNA polymerase and nucleotides and resulting in new copies is not an opinion or inference because the fact is, new more DNA was found in the test tube after adding the enzymes and nucleotides than before the addition. DNA sequencing of the new copies would have shown that the sequences of the new DNA are identical to the original DNA that was first placed in the test tube. Also, other experiments would have shown that adding other different kinds of molecules or enzymes does not, in fact, produce new strands of the original DNA, nor should it be able replicate the DNA at all.
The clue refers to solid data as it was directly witnessed from the experiment. The scientist actually witnessed this data. There was no need for the scientist to make any opinions regarding the information or presume and infer that what would have taken place as he actually witnessed this happening. He witnessed that when DNA was extracted from the cell and was subjected to a test tube with nucleotides and polymerase, the original DNA gets copied.
