单选题 Everyone was obligated to adapt their ways to these overarching rules, as they were commonly understood, and anyone could reasonably judge others, wherever they lived, by their degree of conformity to the ______ principle.
A. fluid B. poignant C. vexatious D. immutable

【正确答案】 D

【答案解析】[解析] D选项：immutable意为“不可改变的”，如：Our nature is not considered immutable，either socially or biologically．(无论是从社会学还是从生物学的角度来看，我们的本性都不是永远不变的。)句意：每个人都有责任根据对这些规则的通常理解遵从这些首要规则。无论身在何方，任何人都可以通过对这个不变规则的遵从程度来合理地评判别人。故选D。
其他三项：fluid流动的，易变的；poignant辛酸的，深刻的；vexatious心烦的，困扰的。