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Similarly one may ask, when should I use which or that?
When To Use “That” and When ToUse “Which” When referring to objects, though, the rule forusing “that” and “which” correctlyis simple: THAT should be used to introduce a restrictiveclause.
Furthermore, when should you use which instead of that?
Rule for using That instead ofWhich The general rule requires that you use that onlyto introduce a restrictive (or defining) relative clause,which identifies the person or thing being talked about. Forexample, The building that I was telling you about is justdown the road.
2 Answers. "Which" is more formal when asking a questionthat requires a choice between a number of items. You canuse "What" if you want, though. Generally speaking,you can replace the usage of "which" with "what" and be OKgrammatically.