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 video projector takes a video signal and projects the corresponding image on a screen using a lens system.

Answer: video projector


Question: aerospace engineering is a field of engineering that specializes in vehicles that move in fluids.

Answer: aerospace engineering


Question: orvon grover autry (september 29, 1907 – october 2, 1998), better known as gene autry was an american movie actor and a singer.

Answer:
gene autry