When ______, the bridge connecting the island to the continent will be open to traffic next year.

【正确答案】 A

【答案解析】时间状语从句的省略形式。当从句的主语与主句的主语一致，且从句有be动词时，从句主语与be动词可以省略，答案为A，完整表达为When the bridge is completed。