English Senior High about 6 yearsago

赤い線の about は副詞だと思うのですが、どうして 副詞句が livesの 主語になれるんですか？ 教えてください！🙇‍♂️

| Im many of the developing countries of Asia and Africa where th 医略記 | urbanization process has only recently begun, about ( )oftn population lives in urban area8. ① one of three ② one-third ② eyery three persons (④ the third