'Which' is used to ask 'which one' or 'which type', usually followed by a noun or a measure-word phrase. 'What' is used to ask about the object, content, or nature of something, often used alone or followed by a noun. 'Which' (as in which one) corresponds to 'which' plus a classifier, and tends to ask 'which one' among a limited set. The differences among the three lie in the scope and structure of the question.

'Which' is commonly used as an interrogative pronoun, followed by a noun to indicate 'which category/type', and followed by a measure-word phrase to indicate 'which one'. In spoken language, '哪+ noun' tends to feel more like selecting a category rather than asking about the essence. 'Which' can also appear in words such as '哪里' or '哪儿' to express location.

'What' is a general interrogative pronoun used to ask about unknown things, content, reasons, or properties. 'What' can function directly as an object, or be combined with a noun to express 'which kind of thing', though the meaning leans toward the entity rather than an option. In conversation, 'what' is often used for open-ended questions, not assuming limited options.

'Which' is typically used to select one item from known or limited options, equivalent to English 'which one'. After '哪个', a noun can follow directly; the context often implies a set of selectable objects. 'Which' places more emphasis on selecting one among a set than '哪+noun', commonly used for objects or people.

When using '哪', the questioner typically assumes the existence of a category or option, even if not explicitly listed. When using '什么', the questioner does not limit the range and expects the content itself. When using '哪个', the questioner assumes selecting one from a group. Choosing the right word can make the question clearer.

'Which' typically appears in the '哪+measure word+noun' or '哪+noun' structures. 'What' can function as a subject, object, or modifier, commonly seen in '什么+noun'. 'Which' often acts as a determiner modifying a noun, and can also serve as a subject or object in questions. Properly choosing the structure helps express a clear question.

When you need to choose among options, prefer '哪个' or '哪+量词'. When asking about the information itself, prefer '什么'. When asking about a category or general class, commonly use '哪+名词'. The key to judging the context is whether you are asking the other person to pick 'one' from a set, or to explain 'what it is'.

The following items compare similar structures and their semantic differences: 'which book' usually presupposes a set of books, while 'what book' leans toward asking about the type or content of a book. 'which restaurant' often selects among known restaurants, while 'what restaurant' asks about the restaurant's nature or kind. 'which person' selects within a group, while 'what person' asks about the type or features of a person.

'Which' tends to select by category or unit and is often followed by a noun or measure word phrase. 'What' asks about the content itself, suitable for open-ended information inquiries. 'Which' emphasizes selecting one from a set, usually corresponding to 'which one'. Choose the appropriate question word according to the scope and goal of the question to make the expression more natural and accurate.