TOEFL Listening: ETS-TOEFL听力机经 - Q8M38A10D6ZE9DK5P$

The professor mentions that a new group of researchers collected samples from a Younger Dryas Boundary site. How did those researchers explain the high concentration of magnetic particles in the samples? A. The Younger Dryas Boundary is especially thick at that site. B. The particles were carried to the site by flowing water. C. A meteor caused a high concentration of the particles at the site. D. Old roofing material had been buried at the site.