参考答案：C

解析：

[分析]： 事实细节的找寻和判断。 根据原文Students may be one answer to Cambridge’s position——as anybody who has entered the university’s myriad common rooms and student bars and witnessed the dense fug of smoke may attest可知剑桥吸烟量名列前茅的原因也许是学生，只要你走进任何一间学校餐厅或学生酒吧就会被浓重的烟雾所包围。由此可见C项内容与原文相符，该项为正确答案。[解题关键] 掌握同义词替换。文中answer与题干中explanation意思相当；而文中the dense fug of smoke显然与heavy smoker密切相关。