The rings of Saturn are comprised primarily of:

The rings of Saturn are primarily made up of ice crystals, which can vary in size from tiny grains to chunks as large as several meters across. This composition is significant because the presence of ice makes the rings very reflective, which is why they appear so bright when viewed through a telescope or even from spacecraft. The ice crystals are mixed with dust and other debris, but the dominant material is indeed ice. Understanding this composition helps to explain many characteristics of the rings, including their brightness, reflectivity, and the way they interact with Saturn's gravitational field.

Other options, such as clusters of small moons, gases, and asteroids, do not accurately describe the primary composition of Saturn's rings. While there can be some small moons and debris within the ring system, they are not the main constituents. Gases are not a significant component of the rings either, as Saturn's atmosphere is separate from the ring structure. Lastly, while some asteroids exist in the vicinity, they do not make up the material that forms the rings. Thus, the choice of ice crystals accurately reflects the primary makeup of Saturn’s rings.