41.Which of the following does the passage mainly discuss? (A) How patterns in rock layers have been used to construct theories about the climate of the Proterozoic age (B) What some rare fossils indicate about glacial conditions during the late Proterozoic age (C) The varying characteristics of Proterozoic glacial varves in different parts of the world (D) The number of glacial episodes that the Earth has experienced since the Proterozoic age