49. Why does the author mention Canada, North America, Africa, India, and Europe in lines 23-24?
(A) To demonstrate the global spread of dropstones
(B) To explain the principles of varve formation
(C) To provide evidence for the theory that there was a global ice age in the early Proterozoic eon
(D) To illustrate the varied climatic changes of the Proterozoic con in different parts of the globe