During the songhai Empire, the songhai people settled along Niger River MAINLY because the river a) gave them fresh water to irrigate crops
b) was a place where people could mine for gold
c) enabled them to easily transport goods to trade

I would have to say B as the answer although in my opinion the multiple choices given make no sense with the historical facts.

Explanation:

Republic of Mexico sought to gain control of its northern reaches, which under the Spanish had functioned as an extensive and largely empty bulwark against encroachment by competing French and British empires to the north. That northern region, which became the state of Coahuila and Texas under the federal system created by the Mexican constitution of 1824, was thinly populated by Mexicans and dominated by the Apache and Comanche Native American peoples. Because most Mexicans were reluctant to relocate there, the Mexican government encouraged Americans and other foreigners to settle there (Spain had opened the region to Anglo-American settlement in 1820). Mexico also exempted the settlers from certain tariffs and taxes for seven years under the Imperial Colonization Law of January 1823. Moreover, though Mexico had banned slavery in 1829, it allowed American immigrant slaveholders to continue using the labour of such.