Which of the following describes the twin planets?

The twin planets refer to Uranus and Neptune, which are often categorized this way due to their similar physical characteristics and composition. Both planets are classified as ice giants because they have a significant amount of "ices" in their atmospheres, such as water, ammonia, and methane, which differentiates them from the gas giants like Jupiter and Saturn.

Uranus and Neptune also share similarities in their atmospheres, including similar temperatures, compositions, and the presence of strong winds and storms. Their size and mass are also comparable, further solidifying their classification as twin planets. In contrast, Mercury and Venus are rocky planets, Earth and Mars have more distinct characteristics due to different environments and compositions, while Jupiter and Saturn are primarily distinguished as gas giants rather than ice giants. Thus, Uranus and Neptune are the pair that most closely represents the concept of twin planets in the solar system.