问题补充：
, the subject was always in my mind.
A. Walking or sleeping
B. Walking or slept
C. Having walked or slept
D. To walk and sleep
答案：
(答案→)A. Walking or sleeping
B. Walking or slept
C. Having walked or slept
D. To walk and sleep
解析：题意为“无论是走路还是睡觉，我总是在想这个问题。”注意：此题中-ing形式短语的逻辑主语与句子的主语并不一致，有的语法家称其为“垂悬分词”。又如：Having suffered such heavy pollution already, it may now be too late to clean up the river. （NMET2001）
