单选题 Tests have proved that caffeine affects the body by increasing the heart rate and rhythm, which ______ affects the circulatory system.
A. in the long run B. in turn
C. in return D. as a result

【正确答案】 B

【答案解析】[解析] in turn“反过来”；in the long run“从长远观点看”；as a result“结果”；in return“作为回报”。本句讲的是咖啡因使心率加快，而心率加快又会影响循环系统，谈论“心率和循环系统的关系及相互作用”，不仅仅是结果，所以B是最佳选择。