我們將探索地球複雜的基礎構造及其支援生命運轉的系統，展示人類面對人為災難和宇宙威脅是如何的脆弱無依。 This special examines our planet's complex infrastructure and life-support systems and shows how humans are vulnerable to attacks from a variety of threats--be it man-made or extraterrestrial.
