Generate a topic word for the given sentence. A topic word is usually the name of a person, place, animal, concept or object the sentence is focusing on.

the nemean lion ( ""; latin: "leo nemaeus") was a vicious monster in greek mythology that lived at nemea.
nemean lion

the british rail class 931 was reserved for former southern region electrical multiple units converted for departmental use.
british rail class 931

hamburg or in full free and hanseatic city of hamburg , is a city in the north of germany on the banks of the river elbe, 18 km away from the north sea.

hamburg