看图，回答问题。

有学者指出，“罗马人”是一个法律概念。从习惯法到成文法、从公民法到万民法，“罗马人”的范围不断扩大，但其核心标准依然是（    ）

Date of birth: July 26. 1985        Weight: 50 kg
Place of birth: Changsha, Hunan    Favorite city: Paris
Height:164 cm                  Hobby: music
Type of blood: AB
   Zhou Bichang was the winner of the Super Girls. She did quite well in her studies and got a high score of 681 in her NCEE in 2003.
Zhou Bichang graduated from Futian High School in Shenzhen and is now a student at the Xinghai Conservatory of Music(音乐学院) in Guangzhou.
   Although her parents gave her a name with the meaning "write excellently" in the hope that she would become a writer. Zhou seems to be a born singer. She could sing theme songs of TV shows very well when she was only two years old. She has more than 4,500CDs.
   Zhou has been well-known across the country during the contest. Fans gave her a nickname "BB" and themselves a title "Chalks". However, BB doesn't seem to enjoy the sudden success. Now she is back to school but feels a bit uneasy when fans see her. "What I really love is singing," said BB in an interview, "but not the life of a star," But that's exactly why "Chalks" love "BB".