Usually, the lenses are darker in the upper part of lenses and gradually to be transparent at the button of the lenses. The purpose of the sunglasses is to protect the eyes fron intensive sunlight, at the same time, allow you see things more clearly through the button part of lenses.
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Answer:
Usually, the lenses are darker in the upper part of lenses and gradually to be transparent at the button of the lenses. The purpose of the sunglasses is to protect the eyes fron intensive sunlight, at the same time, allow you see things more clearly through the button part of lenses.