单选题 ______ in doing an examination, the time passed by quickly.
A. Being absorbed B. Having been absorbed
C. When they were absorbed D. Be absorbed

【正确答案】 C

【答案解析】[解析] 句子大意为：当他们专心投入考试中的时候，时间就过得非常快。本题综合考查语态、时态。可用排除法解题：A项缺主语B项为现在完成时，与主句的过去时不搭配； C项为时间状语从句；D项表述中助动词be的用法错误。所以，正确答案是C。