Choose a word from the list below to complete the sentence.
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arc, centre, circumference, diameter, radius, sector, segment, tangent
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The length of the __________ is double the length of the radius.

The radius is the distance from the centre of a circle to any point on its circumference. The diameter is the distance across the circle passing through the centre. It is made up of two radii joined end-to-end. Therefore, the diameter is double the length of the radius.