A. Because they wanted to agree on certain signs B. As they needed to write them down C. Since they wanted to communicate with each other D. Now that they could combine them 参考答案:C 答案解析:[精解] 文章细节理解题。首先根据题干,可以迅速将该题定位在本文的第一段的第二句"...invented...so that they could communicate with each othe