因为英文单词million是指百万,所以4.5million是450万。 Thus humans who lived a million years ago, despite their big brains and sharp stone tools, lived in constant fear of meat-eating animals . 因此,生活在一百万年前的人类虽然有着巨大的大脑和锋利的石器,却一直生活在对肉食动物的恐惧之中。