Grass is related to Erosion in a particular environmental relationship. In the same way, a Dam is related to which of the following?

Introduction / Context:
This analogy uses real world environmental knowledge. Grass and Erosion appear together in soil conservation, while Dam and the options all relate to water. The question expects you to recognise how grass affects erosion and then apply a similar relationship to a dam.

Given Data / Assumptions:
1) Grass is a type of vegetation that covers soil surfaces.
2) Erosion is the process by which soil or rock is removed by wind, water, or other natural forces.
3) Dams are large structures built across rivers or streams to hold back and control water.
4) The options are Water, Freeze, Current, and Rain, all of which are associated with physical processes.

Concept / Approach:
Grass helps prevent or reduce erosion by binding the soil with its roots and providing a protective cover. Therefore, the relationship can be understood as Grass is used to check or control Erosion. Similarly, a Dam is used to check or control Water, specifically the flow and level of water. Among the given options, Water is the most direct and general term that fits this control relationship.

Step-by-Step Solution:
Step 1: Understand that grass stabilises soil and reduces erosion, so the pair represents controlling or limiting a damaging process. Step 2: Identify that a dam is constructed to control, store, and regulate water in a river or reservoir. Step 3: Examine the options. Freeze is a state change of water. Current refers to the flow of water or electricity. Rain is a form of precipitation. Step 4: A dam fundamentally controls the presence and movement of water itself in a river system. Step 5: Therefore, the closest and most appropriate analogy is Dam : Water.

Verification / Alternative check:
To verify, restate both relationships. Grass helps control Erosion. Dam helps control Water. If you choose Current, you focus only on flow and ignore the broader fact that dams also store water. Similarly, Freeze and Rain are particular conditions or events, not the main quantity being controlled. Water is the central resource that dams are built to manage, so it gives a stronger and more natural analogy.

Why Other Options Are Wrong:
Freeze is about temperature and phase change, not the direct target of the dam. Rain is a source of water but not something dams mainly control. Current is closer, since dams do influence water flow, but the underlying entity is water itself. The original pair grass and erosion focuses on the damaging process, while dam and water focuses on the resource or medium. The standard answer in reasoning questions is Water, which best reflects the main function of a dam.

Common Pitfalls:
A common confusion is to pick Current because people associate dams with hydroelectric power and flowing water. However, dams are not only for electricity; they also store water for irrigation, drinking, and flood control. Choosing Water keeps the relationship broad and consistent with the environmental control idea seen in grass and erosion.

Final Answer:
Thus, the correct completion of the analogy is Dam : Water. Grass is to Erosion as Dam is to Water.