So on Earth, the main outgassing ingredients are pulled out of the atmosphere. On Venus, the H2O never formed an ocean, so it stayed in the atmosphere and eventually escaped. Without oceans, CO2 couldn't form carbonate rocks, so the large amount of CO2 remains in Venus' atmosphere. Furthermore, the seafloor would not disappear so quickly, so more ancient impact craters would be visible. A brief explanation is sufficient.
Tidal heating is probably the main reason.
But odd ices of methane, ammonia, etc. are easier to deform and erupt than previously thought. Briefly summarize Pluto's similarities and differences with respect to the class of object you have chosen. More and more planets are being discovered around other sun-like stars. Explain your answer. SIZE is important because it determines a planet's internal temperature, volcanic activity, and therefore outgassing of an atmosphere and the amount of greenhouse effect.