参考答案

正确答案：If smoking were restricted in public places
If smoking were restricted in public places 解析：If虚拟语气主要用在非真实条件句中。主句would set up表明本句是与现在事实相反的假设，从句用一般过去时。“公共场所禁止吸烟”可以用被动语态表达，即“吸烟在公共场所被禁止”，用smoking were restricted in public places表达。