Which of the following is an example of a solution?

A solution is a homogeneous mixture where one substance is dissolved evenly in another, resulting in a single-phase system. In the case of sugar water, sugar (the solute) is completely dissolved in water (the solvent), creating a mixture that has the same composition throughout. This characteristic of uniformity is essential for classifying a mixture as a solution.

In contrast, oil and water form a heterogeneous mixture in which the two substances do not mix uniformly, leading to distinct layers. Similarly, sand and gravel do not dissolve or blend, resulting instead in separate particles that can be easily identified. Milk, while appearing homogeneous, is actually a colloid, which means it contains dispersed particles that do not fully dissolve. Therefore, sugar water stands out as the only true example of a solution among the given choices.