TOEFL Listening: ETS-TOEFL听力机经 - 3R3J4YX54T1QNVTSP$

What opinion does the professor express when he discusses nanodiamonds? A. Their presence is not strong proof of a meteor impact B. They indicate that a geological sample has been contaminated C. Researchers should get a better understanding of their origin D. Researchers should focus on magnetic particles instead of nanodiamonds