Why is the ocean referred to as the last frontier on Earth?

为什么海洋被称为地球上的最后边疆？

同一单元的其他句子

• The deep sea remains one of the least explored areas on Earth.深海仍然是地球上探索最少的区域之一。
• Have scientists discovered new species in the Mariana Trench?科学家们在马里亚纳海沟发现新物种了吗？
• Exploring the ocean floor requires advanced technology and equipment.探索海底需要先进的技术和设备。
• Do not underestimate the dangers of deep-sea diving.不要低估深海潜水的危险。
• The exploration of the seas has a long and fascinating history.海洋探索有着悠久而迷人的历史。