Which of the following sentences has a gerund?
① Flying planes is not something that he can handle.
② Flying birds are sometimes very dangerous for flights in the air.
③ He depends too much on his wife and even boiling water is out of his mind.
④ Boiling water would make the kettle whistling.
句意：下面哪些句子含有动名词？动名词做主语，后面动词用第三人称单数形式。由此可判断① 中的flying是动名词，② 中的flying是形容词。boiling water中的boiling是形容词，故③ 不正确，④ 中的 whistling是动名词，做宾语补足语。因此，本题的正确答案为A。