A

Step 1: Understand the concept of capillarity. When one end of a capillary tube is dipped into water, the adhesive force between the water molecules and the walls of the tube causes the water to climb up against gravity.

Step 2: The curvature of the meniscus (the surface of the water in the tube) creates a pressure difference. According to the Young-Laplace equation, the pressure below the meniscus is less than the pressure outside due to surface tension.

Step 3: This pressure difference is essential for the upward movement of water in the tube. The adhesive forces (attraction between the tube and water) are stronger than the cohesive forces (attraction among water molecules), resulting in the rise of water.

Therefore, the correct answer is: A: Pressure below the meniscus is less than atmospheric pressure.