Which of the following most logically completes the passage? A. the use of fire might have originated independently in several different parts of the world B. it is possible that fire was used much earlier than 500,000 years ago C. the charred rocks found in the deposit included several different kinds of stone, all of which are common in the immediate vicinity of the site D. animal bones could have been discarded in a fire used for purposes such as protection or heat rather than for cooking E. it is impossible to determine whether a charred deposit dating from so long ago resulted from a fire caused by lightening or from the purposeful use of fire