冷漠的儿子今年多大了

　　Mount Rushmore is one of America's most iconic landmarks, but there are dark mysteries behind its presidential faces; experts use cutting-edge tech and the latest science to reveal what lies beneath the rock and the secret history of its creation. 　　拉什莫尔山雕刻着美国四名总统的花岗岩头像，这是世界上知名度最高的地表景观之一，本集要挖掘这座现代建筑奇迹隐藏的秘密，它的建造秘诀是什么？为什么要把美国最著名的地标景观选址在偏远的南达科他州？