iii. works the most.B. ii. works the most.C. They work the same way.D. Not sure. 18. Regarding friction and work, which of the following statements is TRUE?A. Sliding friction always does negative work.B. Sliding friction can do negative and positive work.C. Static friction must do negative work on the object.D. Static friction always does positive work on the object.19. Which of the following statements is TURE?A. The pole vault record is 6m, which is much higher than the normal high jump record; this is because the gravitational potential energy of the body is transformed into kinetic energy.B. Pile stacking uses kinetic energy instead of gravitational potential energy.C. Modern large-scale hydroelectric power plants transform gravitational potential energy into kinetic energy to produce electricity. D. A sled slid down a mountain and transferred kinetic energy to gravitational potential energy.20. There is a small ball whose mass is m and it is moving on a flat, smooth surface, which has height H, at a speed v. When it leaves the flat surface and rolls along an inclined plane, it passes the point At what height is h. When the small ball passes point A:A. Its gravitational potential energy is mg