单选题 People will find themselves suffering from headache and watering eyes, and even snowblindness, when ______ to several hours of "snow light".
A. being exposed B. having been exposed
C. exposed D. exposing

【正确答案】 C

【答案解析】[解析] 相当于when they are exposed to...。在when，if，unless，though，while，once引导的从句中，如省略，必须将主语与be动词一起省掉。另外，“人们被置于雪光中”，是被动语态，所以D是错的。