Bulk-solids conveying equipment is grouped by what produces the motion of the load-carrying element. Belt-type or chain-type conveyors share one feature: an endless flexible loop is driven by a head pulley or sprocket, and the load-carrying attachments (pans for apron, buckets for bucket, flights for scraper) simply ride along on that loop.
A screw conveyor works differently: a helical screw keyed to a rotating shaft advances material trapped between the trough and the helix. There is no endless loop of any kind anywhere in a screw conveyor.
Sorting the four options by drive principle: apron, bucket, and scraper conveyors all belong to the chain-conveyor family, while the screw conveyor belongs to the separate screw conveyor family.