He might not have been killed in the traffic accident yesterday if he (fasten) 1 the seat belt.
【正确答案】
1、正确答案：had fastened
【答案解析】解析：本题考查的是if引导的条件状语从句中的虚拟语气。表示与过去事实相反的假设，用的句式为“if+主语+had done，主语+would／should／could／might+have done”。如：If you had come earlier，you might have met him．(如果你早点来，就能遇见他了。)