B

Step 1: Understand the concept of meniscus: When a liquid is in contact with a solid, the shape of the liquid's surface can change based on the adhesive forces between the liquid and solid and the cohesive forces within the liquid itself.
Step 2: For a liquid that wets a solid completely, the adhesive forces between the liquid molecules and the solid surface are stronger than the cohesive forces among the liquid molecules.
Step 3: This results in a meniscus shape where the liquid curves upward towards the solid.
Step 4: In a sufficiently long tube (like a capillary tube), this leads to a concave meniscus.
Conclusion: Hence, the meniscus of the liquid in this situation is concave.
Therefore, the correct answer is B.