Sentence examples for is which from inspiring English sources

"is which" can be used in written English.
It is often used as part of a question or to introduce a clause that provides more information or clarification. Example: "The main ingredient in this dish is which vegetable?" In this example, "is which" is used to ask for more specific information about the vegetable being used in the dish. "Her favorite movie, is which she has seen multiple times, is being remade." In this sentence, "is which" introduces a clause that adds more detail about the subject (her favorite movie) and provides further context for the main sentence.