【正确答案】 C

【答案解析】事实细节题。由“natural law”出现的前——句话You found upon that a general law，that all hard and green apples are sour；and that，so far as it goes，is a perfect induction．可知这个“自然规律”就是指前面刚刚提到的归纳结果——“又青又硬的苹果都是酸的”。