疑问代词“怎么”：问原因

在HSK 1里，“怎么 + 动词”问方法，比如“这个字怎么读？”。“怎么”也可以问原因，意思和“为什么”差不多，可是常常表示说话人觉得奇怪、没想到。“怎么”放在主语后面、动词或形容词前面，比如“你怎么不吃了？”。

You already know 怎么 + verb asking HOW to do something (这个字怎么读?). 怎么 can also ask WHY — like 为什么, but with a note of surprise: "How come …?" The speaker has noticed something unexpected. It goes after the subject and before the verb or adjective, and often comes with 不 / 没 / 还 / 这么: 你怎么不吃了? (How come you've stopped eating?), 他怎么还没来? (Why isn't he here yet?). Use 为什么 for a neutral question about reasons; use 怎么 when you're surprised.