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.

[EX Q]: in greek mythology, the nereids ( "nereides") are sea nymphs, the fifty daughters of nereus, the old man of the sea, and the okeanid doris.
[EX A]: nereid

[EX Q]: the kiwi is a bird from new zealand.
[EX A]: kiwi

[EX Q]: the diplura are a biological order.
[EX A]:
diplura