They borrow the characters from what had been already something quite close to an alphabet and had only a relatively small number.

他们从十分接近字母系统的书写体系中,借来字符使用,而这些字符相对较少

耶鲁公开课 - 古希腊历史简介课程节选

I forget the exact number of the ones in the Semitic alphabet, but we're talking about roughly twenty-five.

我忘了闪米特语中有多少字母,粗略说来大概有二十五个

耶鲁公开课 - 古希腊历史简介课程节选