1, the blade rotates around the center: there are countless straight lines behind a point.

2. Triangle bracket: Triangle has stability.

3. Quadrilateral sliding door: Quadrilateral instability.

4. Functional relationship among speed, time and distance.

5. Use coordinates to indicate geographical location.

Whether you can win the lottery is a question of probability.

7. The smooth flight of kites is the application of the nature of axisymmetric graphics.