Across
2. resting place of pharoah
6. legendary sumerian king
8. union of several peoples under one ruler
10. an egyptian god-king
11. series of rulers from a single family
| 13. first chinese dynasty to produce iron
14. river in the fertile crescent
15. world's longest river
16. first chinese rulers to leave written records
early river valley civilizations crossword puzzle ()

i think the answer is c, rivers.

explanation:

sometimes, borders fall along natural boundaries like rivers or mountain ranges. for example, the boundary between france and spain follows the crest of the pyrenees mountains. for part of its length, the boundary between the united states and mexico follows a river called the rio grande. the borders of four countries divide africa’s lake chad: niger, chad, cameroon, and nigeria.

really and truely i dont know sorry

the indians crossed artificial boundaries, setting the stage for conflict

silk

indigo  

rice

all the other answers are wrong