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.

[Q]: jeong mong-ju (, hanja:鄭夢周, 1337 - april 1392) was a korean goryo dynasty politician, writer, poet and thinker.
[A]: jeong mong-ju


[Q]: a group of his hostages nicknamed him "jihadi john" since he was part of a four-person terrorist cell with british accents whom they called "the beatles".
[A]: jihadi john


[Q]: the sei whale ("balaenoptera borealis") is a dark-gray, stream-lined baleen whale that is found worldwide except in polar waters.
[A]:
sei whale