1. Mars is too faint and too low in the sky to be observable. 火星太暗，在空中位置太低，所以观测不到。
2. In contrast, high-frequency fluctuations such as seasonal temperature variations are observable and somewhat predictable, so that groups could have adapted their behaviors accordingly. 相反，诸如季节性温度变化等高频波动是可以观察到的，而且在某种程度上是可以预测的，因此群体可以相应地调整它们的行为。
3. Some archaeological sites have always been easily observable—for example, the Parthenon in Athens, Greece; the pyramids of Giza in Egypt; and the megaliths of Stonehenge in southern England. 一些考古遗址一直很容易被观察到——例如，希腊雅典的帕特农神庙、埃及吉萨的金字塔以及英格兰南部的巨石阵。
4. Similar trends are observable in mainland Europe. 类似的趋势在欧洲大陆也能见到。
5. It's not an externally observable characteristic unless you want to flaunt it. 除非你想炫耀它，否则它不是一个外在可见的特征。
