问题详情

Perhaps all societies (are significantly more advanced) than our own have achieved an effective personal immortality and lose the motivation for interstellar gallivanting, which (may), (for all we know), (be) a typical urge only of adolescent civilization
A．are significantly more advanced
B．may
C．for all we know
D．be请帮忙给出正确答案和分析，谢谢！