TOEFL Listening: ETS-TOEFL听力机经 - XZBAU75DZ934414OP$

What point does the professor make about closely related plants such as wheat and barley? A. It was impossible to see the differences in the shape of their phytoliths until recently B. Their seeds can be identified using election microscopes C. It was unknown until recently that their phytoliths decay at different rates D. Their phytoliths are typically found it in vessels used for cooking