Answer:
living things respire to get oxygen for living cells to function. Without air, there is no life. Plants use Carbon Dioxide (together with sunlight and water) to produce energy and give out Oxygen as a by-product. This oxygen is what almost all animals need to survive.
Explanation:
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Fingernails are made of protein and keratin. Gypsum is softer than a fingernail.
Answer:
Alloy is a mixture made up of iron &nickel.