Today's Mars is in stark contrast to its early history. Early Mars was warmer and wetter, and perhaps then more suitable for life. Future Mars exploration will dig deeper into evidence of life, and those lives may still be on Mars. Take refuge under the ground. Which of the following is presupposed by the above discussion? ['Early Mars could have life.', 'The surface of Mars is not suitable for any life.', 'Today, Mars may still have a different living environment than the surface.', "The ice on the surface of Mars may be leftover from Mars's warm and humid environment in the early days."]