Digital SAT Reading and Writing Practice Question #301

Radiocarbon dating of artifacts from the ancient Mesoamerican city of Teotihuacan shows that the foundational construction of the massive Sun Pyramid occurred nearly concurrently with a sudden demographic shift in the surrounding basin. For decades, many archaeologists hypothesized that a catastrophic volcanic eruption in the southern valley triggered a sudden migration into Teotihuacan, creating the immense labor force required for the pyramid's rapid urbanization. However, recent high-resolution geological core samples from the southern basin indicate that the volcanic eruption deposited primary ash layers exactly concurrent with the *completion* of the Sun Pyramid, but significantly *after* its foundational stages were laid. Which of the following most logically completes the text?