生活在高原上的人，与生活在平原地区的人比较，血液中含的红细胞数量多，这是长期与下列哪项生态因素相适应的结果（　　）

     Tony Wheeler was born to travel. His father worked for an airline. For the first 16 years of his life，Wheeler and his family lived in many different countries.
     In the early 1970s，Wheeler met a young woman named Maureen. They soon married. Before getting jobs， Tony and Maureen wanted to travel. They took a year-long trip from London，through Asia，to Australia. On the trip，they visited places like India， Iran， and Afghanistan.
     When Tony and Maureen arrived in Australia，people asked many questions about their trip. To answer these questions，Wheeler wrote a guidebook called Across Asia on the Cheap . The book told people about different countries' weather，customs(风俗），and places to see. But unlike travel guides in the 1970s，Wheeler’s book also talked about places most tourists did not go. He also wrote about unusual things to see and do. The book was very popular．
     Wheeler and Maureen started a company called Lonely Planet. They continued travelling. They wrote guidebooks for each place they visited. Today，400 people work for Lonely Planet. The company has over 650 guidebooks. Wheeler still writes about travel “hot spots” (for example，Cambodia in Asia and Croatia in Europe). For more information，read the books!

抬升指数是一种表示大气对流性不稳定的指数，指一个气块从地面出发，上升到500百帕（海拔5500米左右高度）处所具有的温度被该处实际大气温度所减得到的差值。读下图某区域某时刻抬升指数等值线分布图，完成下列各题。