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 alkaline earth metals are the second group of metals on the periodic table.

Answer: alkaline earth metal


Question: an electronic book (also called an e-book, ebook or digital book) is a book in digital form.

Answer: e-book


Question: warfarin (or brand name "coumadin") is a powerful water-soluble compound.

Answer:
warfarin