单选题 .  ①According to the prevailing view, Homo erectus, an ancestor of Homo sapiens, lacked the intellectual and technological sophistication to have achieved controlled use of fire; that had to wait for the emergence of H. sapiens 40,000 years ago. ②However, recent evidence seriously undermines this view. ③At two sites in Kenya, many small, lens-shaped patches of discolored earth were uncovered along with bones and stone tools of H. erectus. ④Analysis showed that the patches, which, like the tools and bones, dated from 1.6 million years ago, were almost certainly the result of deliberately built fires, since those fires were evidently much hotter than typical naturally occurring bush fires. ⑤The size of the patches rules out lightning strikes, which could have explained the fires ' high temperatures. ⑥Furthermore, the fires were fed by a mixture of grasses and woods that strongly deliberately collected fuel. ⑦In addition, many of H. erectus' tools were made of basalt or quartz, stones when exposed to the intense heat near a campfire, form characteristic dimples on their surface. ⑧A recent study found that such dimples never appear on tools dating earlier than 1.6 million years ago but do consistently appear on later tools.35.  The primary purpose of the passage is to ______