Circle 1: Turn it into a donut by adding icing and sprinkles.
Circle 2: Create a clock face.
Circle 3: Make it a steering wheel by adding spokes.
Circle 4: Turn it into a face by adding eyes, a nose, and a smile.
Circle 5: Design a basketball by adding lines to indicate the texture.
Circle 6: Sketch a flower with petals emanating from the circle.
Circle 7: Make it a globe by sketching continents.
Circle 8: Design a bicycle wheel.
Circle 9: Turn it into a pizza with toppings.
Circle 10: Draw a camera lens.
Circle 11: Make it the face of a clock with numbers.
Circle 12: Sketch a sun with rays.
Circle 13: Create a pool ball.
Circle 14: Draw a coin.
Circle 15: Sketch a globe or a planet.