iii. works more.B. ii. it works more.C. They work the same way.D. Certainly not. 18. Regarding attrition 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 6 meters, 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 driving 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 sliding down a mountain transfers kinetic energy to gravitational potential energy.20. There is a ball whose mass is m and moves on a flat and smooth surface, of height H, with speed v. When it leaves the flat surface and rolls down an inclined plane, it passes through point A at which height is h. When the ball passes the point A:A. Its gravitational potential energy is mg