Although the earliest surviving Greek inscriptions written in an alphabet date from the eighth century B.C., a strong case can be made that the Greeks actually adopted alphabetic writing at least two centuries earlier. Significantly, the text of these earliest surviving Greek inscriptions sometimes runs from right to left and sometimes from left to right. Now, the Greeks learned alphabetic writing from the Phoenicians, and in the process they would surely have adopted whatever convention the Phoenicians were then using with respect to the direction of writing. Originally, Phoenician writing ran in either direction, but by the eighth century B.C. it had been consistently written from right to left for about two centuries.
In the argument given, the two portions in boldface play which of the following roles?
虽然希腊石碑上的字是来自公元前8世纪的,但根据石碑上面的字有的从左写有的从右写可以推断,希腊人至少是在公元前10世纪就学会了alphabetic的写法。希腊人学写alphabetical的字是从P人种哪里学的,而P人种从公元前8世纪就只是从右边往左边写了,所以希腊人肯定不是公元前8世纪才学alphabetical的字的,是更早还没有顺序的时候学的。两个黑体字部分都是在论证“希腊人公元前10世纪学字母法写字”这个结论。