Overview:
Surface tension is a phenomenon that occurs due to the cohesive and adhesive forces between the molecules of a liquid. Both these forces play a role in giving rise to surface tension. Therefore, the correct answer is option 'C'.

Explanation:
Cohesive Force:
- Cohesion refers to the attractive force between the molecules of the same substance.
- In a liquid, the molecules are in constant motion and are attracted to each other.
- These cohesive forces create a net inward force on the molecules at the surface, pulling them towards the bulk of the liquid.
- This results in the formation of a "skin" on the surface of the liquid, which is known as surface tension.

Adhesive Force:
- Adhesion refers to the attractive force between the molecules of different substances.
- When a liquid comes into contact with a solid surface, adhesive forces exist between the liquid molecules and the molecules of the solid.
- These adhesive forces can also contribute to surface tension by pulling the liquid molecules towards the solid surface.
- This can be observed when a liquid wets a solid surface and forms a meniscus, such as in a glass capillary tube.

Combined Effect:
- Both cohesive and adhesive forces contribute to the overall surface tension of a liquid.
- The cohesive forces between the liquid molecules create a "stretching" effect at the surface, which resists any external force or deformation.
- The adhesive forces between the liquid and a solid surface enhance this stretching effect and can cause the liquid to rise or be depressed at the solid-liquid interface.
- The combined effect of these forces gives rise to surface tension, which allows certain insects to walk on water, causes the formation of droplets, and enables capillary action, among other phenomena.

In Conclusion:
- Surface tension is a result of both cohesive forces between the liquid molecules and adhesive forces between the liquid and a solid surface.
- These forces work together to create a "skin" on the surface of the liquid, giving rise to surface tension.
- Therefore, the correct answer is option 'C' - both cohesive and adhesive forces contribute to surface tension.