In today's era, our labor can be divided into two parts: one is the labor paid to obtain the means of living necessary for survival today; the second is the labor paid in advance for future development. When the ratio of the two is greater than the latter, It shows that our labor is still at a lower level; when the latter is much larger than the former, it means that our labor level has been greatly improved. Therefore, only through social development, progress, and improvement of people's efficiency and level can we truly achieve The complete liberation of humanity itself. What is the correct understanding of this passage? ['To make our society develop faster, we must do more labor that is paid in advance for future development.', 'An important sign of the development of human society is the improvement of the level of labor.', "In modern society, any person's work can be divided into two levels.", "In today's era, the purpose of our labor is mainly to obtain the means of living necessary for survival."]