问题
单项选择题
Most of the older civilizations which flourished during the fifth century B.C. are died out .
A．they have died out
B．has died out
C．have died out
D．they had died out
答案
参考答案：C
解析：结构应用。本句是个复合句：Most of the older civilizations是主语，后面是which引导的定语从句which flourished during the fifth century B.C. 因此划线部分应是谓语动词；根据主语，谓语应用复数形式；因此选项C正确。