It follows from the theory of the role of carbon dioxide discussed in paragraph 6, that A. the decrease in temperature during the last ice age caused a decrease in atmospheric carbon dioxide B. the atmosphere had higher carbon dioxide content during the last ice age than it had during the warm period immediately before it C. the cooling of temperatures that led to the last ice age was brought about by a decrease in atmospheric carbon dioxide D. there was less carbon dioxide in the atmosphere toward the end of the last ice age than there was at the beginning