Some people here said they had ________ a boy in blue near the stop. But where can he be?
A.found; to playB.seen; playC.found; playingD.seen; playing在线课程B
解析：
根据后文可知，这个孩子还未找到，所以不论found还是seen后都不能跟现在分词，句意应为“发现”或“看见”“在车站附近玩过”，而没有“find sb. to do sth.”结构，故选B。