TOEFL Listening: ETS-TOEFL听力机经 - DD34WH6X51ZOE318P$

What did researchers conclude by studying the signs in the oldest caves? A. The signs were already being used by the people who migrated to the area. B. The signs were developed in southern France. C. The creation of the signs was a slow, gradual process. D. The development of the signs occurred at about the same time as the development of paintings.