Correct Answer 1a. Correct. 1b. Grammatically possible but sounds unnatural. Avoid it. 2a. Correct. 2b. Grammatically possible but very unnatural. Don’t use it. 3. Correct and natural: “They’ve been friends for I don’t know how long.” 4. Needs fixing: Correct version: “He would be hungry long before a breakfast coming from he-knew-not-where.” More natural modern English: “He would be hungry long before breakfast that came from who-knows-where.” Teaching Tip These “inverted” structures exist, but they sound old-fashioned. For clear modern English, always keep normal word order.

I think if you add hyphens it makes a little more sense: He came from nobody-knew-where. He lives who-knows-how. And so on. These phrases basically replace the word or phrase that would usually be used to describe the situation, but in this case these specific descriptions are unknown to the speaker. For example a correct sentence would be: He came from Ohio. "Ohio" is replaced with the phrase "nobody-knew-where," either because nobody knew where he was from, or because he's from some obscure, small and mostly unknown town that nobody could remember, even though they've been told before. And that's the way these phrases are used: to say that nobody knows this particular fact for one of these two reasons. Either because nobody knows or because it's difficult to remember or imagine. It's a stylistic device to express this circumstance. The phrase "who/nobody-knows/knew-wh-question" is used as a place holder for a single word or another phrase that would be used if the circumstance was known. I hope this helps.