....................... is a self adjusting force

Self-adjusting force is defined as a force which can adjust itself  as required by the situation.

 It can increase or decrease itself with the change made in the system.

 If the surface of two bodies are in contact with each other and force on one of them, static friction will appear, even if the body is at rest.

The static friction will try to make the body to remain at rest.

 An  external force on the body the static friction will adjust the magnitude of friction force and try to make the object to remain at rest.

It has a limit between  is the normal reaction and μ is coefficient of friction .

It opposes the externally applied force between these limits.

 So, static friction is a self-adjusting force because it does not have any fixed magnitude, but it will adjust the force according to the applied force.

Hence , option (c) is correct. ( Frictional Force )