I. The frictional force is independent of the area of the surfaces in conduct II. The frictional force depends on the nature of the surfaces in contact III....

The question is asking which of the given statements are true for sliding friction. I. The statement that "The frictional force is independent of the area of the surfaces in conduct" is false for sliding friction because the frictional force depends on the area of surfaces in contact. II. The statement that "The frictional force depends on the nature of the surfaces in contact" is true for sliding friction because the amount of friction generated between two surfaces depends on their nature or texture. III. The statement that "The frictional force depends on the speed of sliding" is also true because the amount of friction changes with the speed of sliding. IV. The statement that "The frictional force is directly proportional to the normal reaction" is true because the amount of frictional force is directly proportional to the normal reaction between the two surfaces in contact. Therefore, the combination of statements that are true for sliding friction is: I, II and IV