Task: Question Generation
Input (English): The four main dialectal forms of Old English were Mercian, Northumbrian, Kentish, and West Saxon. Mercian and Northumbrian are together referred to as Anglian. In terms of geography the Northumbrian region lay north of the Humber River; the Mercian lay north of the Thames and South of the Humber River; West Saxon lay south and southwest of the Thames; and the smallest, Kentish region lay southeast of the Thames, a small corner of England. The Kentish region, settled by the Jutes from Jutland, has the scantiest literary remains.
Output (English): Geographically, what river was Northumbria north of?