国家开放大学 / 综合英语（1）
正确率：100%
One of the reasons why men invented certain sounds to express thoughts and actions
was that they could _ _ _ _ _ _ .
a. agree with certain signs
b. write them down
c. make themselves understand each other
d. combine them
was that they could _ _ _ _ _ _ .
a. agree with certain signs
b. write them down
c. make themselves understand each other
d. combine them
参考答案：
佳题速递：