1. When did my teacher retire? [a time word appears before the verb “to retire”]
2. Why is he still very busy? [the info might appear after yīnwèi]
3. How can the new book help us? [the info might appear after the verb “to help”]
4. Why doesn’t the bookshop have my teacher’s books? [try to pay attention to the clause before suǒyǐ]