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.
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Question: a hospital ship is a big boat which is built to cure patients.

Answer: hospital ship


Question: nelsan ellis (november 30, 1977 – july 8, 2017) was an american actor and playwright.

Answer: nelsan ellis


Question: plankton are drifting organisms that live in the surface layers of the ocean.

Answer:
plankton