The correct answer is: D. force of cohesion.
The force of cohesion is the attraction between molecules of the same substance. It is a strong force that holds the molecules together and prevents them from flowing past each other. This force is what causes the surface of a liquid to behave like a sheet and tend to contract to the smallest possible area.
The force of adhesion is the attraction between molecules of different substances. It is a weaker force than cohesion, but it can still be significant. Adhesion is what causes water to stick to a glass surface, for example.
The force of friction is the resistance to motion between two surfaces that are in contact. It is caused by the roughness of the surfaces and the interlocking of the molecules on the surfaces. Friction can be a significant force, but it is not the force that causes the surface of a liquid to behave like a sheet.
The centrifugal force is a force that is felt by objects that are moving in a circular path. It is caused by the acceleration of the object towards the center of the circle. The centrifugal force is not the force that causes the surface of a liquid to behave like a sheet.