Air is an invisible substance that envelopes the earth. Living things on the earth's surface depend of it for their survival. Air is vital to plant and animals. Without air, a human being cannot live more than a few minutes.Some animals like whales can hold their breath for many minutes when they dive into the sea. However, eventually they will still have to come to the surface to breathe.
This substance air consists of a mixture of gases. Normally,air is made up of about 70% oxygen, 20% nitrogen
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