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Paul: Alex, help me, please. This pipe is very heavy.
Alex: 1_______? What material is it made of?
Paul: Actually, it is made of metal.
Alex: Why is it made of metal?
Paul: Well, because it is a strong material. 2_______, it is stronger and more rigid than rubber.
Alex: 3_______?
Paul: 4_______. It is the most expensive material, as a matter of fact.