The statement that best shows how river valley civilizations built upon existing Neolithic technology is: "River valley civilizations added new tools in addition to stone tools from the Neolithic period and expanded on preexisting knowledge of metallurgy."
This option accurately reflects how these civilizations not only continued to use existing technologies from the Neolithic era but also innovated by introducing new tools and advancing their understanding of materials, particularly metallurgy, which played a crucial role in their development and expansion.