第3题: [单项选择]Tuberculosis is highly infectious because ______. A. spores are resistant to drying B. the causative organism is encapsulated C. droplets of sputum remain infective for a long time due to the resistance of the organisms to drying D. none of these 参考答案:C 答案解析:根据文章最后一句可知上呼吸道感染细菌在干燥空气中存活的时间长是导致其具有极强的传染性的原因。