10. Which factor most likely determined the boundaries of these provinces?

Ithink the answer is d.

Are there choices? it would really me you me to answer this question : ). if not then here is a list of rivers that i got online, i will leave a link so that it isn't copyright : ). irrawaddy river, salween river, chao phraya, mekong, and read rivers.   and here is the link: if this , let me know, and mark brainliest, s much : )dear i hope this is not against your rules, i am just trying to my good friend billystofan : )