Cob has been used since the 17th century as a building material. It is made by mixing dry sand, sifted clay and water. A cob house is a house that is made from this material. A benefit of using this material, is that it is sustainable and only uses natural products.
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fact or situation that is observed to exist or happen, especially one whose cause or explanation is in question
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I think the answer is D, because claims are, essentially, the evidence that writers or speakers use to prove their point.
in order to answer question, need to read an look at the passage