单选题 The bones, tendons and cartilages require a small amount of blood, ______ such organs as the kidneys and brain need large amounts of blood.
A. as B. while C. because D. so that

【正确答案】 B
【答案解析】[解析] 连词用法辨析
连词while可以连接并列关系的分句，微含“转折”之意，符合题意。