TOEFL Listening: ETS-TOEFL听力机经 - 4NW893T1Q5W13IENP$

What point does the professor make when he talks about under drawings? A. They are primarily used by artists who wanted to execute an exact copy of an early painting B. They are usually highly detailed C. They can be used to distinguish an original painting from a painting D. They can reveal whether a wood panel was reused by an artist.