Leading:人类一直努力寻找宇宙中的其他生命迹象,至今未果.但最近美国国家航空航天局的最新发现似乎意味着一些实质性进展。 For decades,looking for life elsewhere in the universe meant listening for signals that could be from distant civilizations. But recent breakthroughs in space technology refocused some of that effort toward finding planets that may harbor life, even in its primitive form.