Sustainability is not an option; it's a necessity for the future of agriculture.
可持续性不是一种选择；它是农业未来的必要条件。
The existence of a legal system depends on the acceptance of secondary rules by officials.
预测未来的唯一方法就是创造未来。
The anarchic nature of the international system forces states to compete for power.
如果我们想保护森林，就必须先了解它们。