Five children spin around on a playground roundabout ; three lay on their backs , while one attempts to pull himself up with both arms , and another holds onto the side while sitting up .
It is certain that children are playing on a merry-go-round .
It is certain that children are playing on a merry-go-round .
It is probably not the case that children are playing on a merry-go-round .
Children are playing on a merry-go-round .