A real gas most closely approaches ideal behavior under which of the following conditions?

When a sample of gas is compressed at constant temperature from 15 atm to 60 atm, its volume changes from $76\,\,{\rm{c}}{{\rm{m}}^3}\,\,{\rm{to}}\,\,20.5\,\,{\rm{c}}{{\rm{m}}^3}$. Which of the following statements are possible explanations of this behaviour? 1. The gas behaves non-ideally. 2. The gas dimerises. 3. The gas is absorbed into the vessel walls.