the police were told that some boys were seen_ on the streetA to play B.playing C.to be playing D played.

the police were told that some boys were seen_ on the streetA to play B.playing C.to be playing D played.
the police were told that some boys were seen_ on the street
A to play B.playing C.to be playing D played.

the police were told that some boys were seen_ on the streetA to play B.playing C.to be playing D played.
这个句型是see somebody doing sth,看见某人正在做某事改成被动的话,就是某人被看见正在做某事 就是B选项中的 some boys were seen playing on the street

B，状语

绝对b