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Solve the following problem using Python, implementing the functions described below, one line at a time
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Description:
 def make_simple(self):
 """ Return a cylinder with the thread's average radius & length. :math:`radius = (inner_radius + outer_radius) / 2` """

        (inner_radius, outer_radius) = self.get_radii()
        radius = (inner_radius + outer_radius) / 2
        return cadquery.Workplane('XY') \
            .circle(radius).extrude(self.length)