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.

theoxena scissaria is a species of moth.
theoxena scissaria

the river trent is one of the major rivers of england.
river trent

friedrich ostermann (21 june 1932 — 22 october 2018) was a german roman catholic official.

friedrich ostermann