When I passed this afternoon I saw a little boy was lying on the grass his hands under

问题补充：

When I passed this afternoon, I saw a little boy was lying on the grass, his hands under his head.

A. having crossed

B. crossing

C. crossed

D. to cross

答案：

A. having crossed

B. crossing

(答案→)C. crossed

D. to cross

解析：句意：当我今天下午路过的时候，看见一个小男孩躺在草地上，他的双手交叉放在头底下。这里整个句子一个when引导的时间状语，I saw a little boy was lying on the grass这是主句；his hands crossed under his head是独立主格结构，cross ones hands, 交叉手臂；这里his hands与cross之间是被动关系，独立结构sth+done，这里的sth与done之间是被动关系，故选C。