The little boy was last seen______football by the river.

问题描述:

The little boy was last seen______football by the river.
A.to play B.play C.played D.playing

选D吧.强调 那个男孩最后一次被看见的时候正在踢足球

如果选A的话强调男孩整个踢球过程被看见 与语境不太相符

是这样吧