For the next 1,800 miles the thin blue ribbon of the Nile, flowing slowly north, unwound over brown soil and green fields, some only a few yards wide, others as broad as an Iowa cornfield.
请问some only a few yards wide, others as broad as an Iowa cornfield在句中作什么成分？
some only a few yards wide中some和only a few yards wide是什么关系？
others 和as broad as an Iowa cornfield是什么关系？
