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: the british rail class 931 was reserved for former southern region electrical multiple units converted for departmental use.

Answer: british rail class 931


Question: stornoway airport is an airfield on the outer hebrides isle of lewis.

Answer: stornoway airport


Question: northern illinois university is a public university in dekalb, illinois.

Answer:
northern illinois university