* Suspensions are mixtures where solid particles are dispersed throughout a liquid. The particles are large enough to be seen with the naked eye and will settle out over time.

* Gravel is too large to be considered a suspension. It's a solid material that will simply sink to the bottom of the water and form a separate layer.

Here are some examples of suspensions:

* Muddy water: Tiny soil particles are suspended in the water.

* Milk: Fat droplets are dispersed throughout the water.

* Sand in water: Sand grains are suspended in the water.

Therefore, water and gravel would be considered a heterogeneous mixture where the two components (water and gravel) are distinct and separate.