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 7 july 2005 london bombings (also called 7/7) were suicide bomb attacks aimed at london's public transport system during the morning rush hour.

Answer: 7 july 2005 london bombings


Question: abraxas grossulariata is a moth of the family geometridae.

Answer: abraxas grossulariata


Question: pella is one of 51 prefectures of greece.

Answer:
pella