There have been no immortal people since ancient times, but each person's life expectancy is very different. From the perspective of biology and medicine, human life expectancy should have a biological maximum, but it is not yet possible to determine the maximum human life expectancy How tall. What does this passage mainly support on human lifespan? ['is infinite.', 'How high is the space we cannot know.', 'There should be limits, but they have not yet been found.', "It's different for different people."]