In the following question, a sentence is given with certain words in bold. Choose the pair/s of such words which need to be interchanged so as to make the sentence grammatically correct and meaningful.

A significant number of hearths have been (A) unearthed around the 76,000-year mark and there is (B) controlled archeological evidence of (C) diminishing fire the further back you go, so the (D) assumption is that once we became modern, we worked out how to cook.