现在地球上许多珍稀物种正在灭绝，因为它们无法繁殖。当自然繁殖失败时，科学开始介入。比如，科学家们正在试图帮助大熊猫、黑足雪貂，还有这只可爱的云豹。不过，要想让一对成年云豹自然交配，而不是互相攻击，实在是个难题……...

We all know the main story of Abraham Lincoln's death, how he was killed, where it took place, and who pulled the trigger. But what exactly happened during the last day of his life? Relive April 1...