This means going back to the place where we left the family in a tree the night before.
A. to sleep
B. to be sleeping
C. slept
D. sleeping
网友回答
A. to sleep
B. to be sleeping
C. slept
(答案→)D. sleeping
解析： 考查非谓语。the family与sleep为主谓关系所以用现在分词作补语。句意：这意味着我们要返回前天晚上这一家睡觉的地方。