Why did american settlers in texas have conflict with the mexican government during the 1830s?

a.
american settlers owned slaves, which violated mexican law.

b.
the mexican government insisted that settlers move to territory farther south.

c.
the mexican government refused to allow settlers to establish farms or ranches.

d.
american settlers who were catholic could not vote or own property.

The best answer here is A, a huge conflict between the Mexican government and American settlers was slavery.  Leading up to the Mexican American War 
(1846-1848), the Mexican government started creating and enforcing more laws surrounding American settlers, as they were becoming very numerous.  Even after the war, slavery was still an issue for settlers in Texas (which became independent after the war) and this contributed to the civil war.  Hope this helps!

February 1848 is when it was added. if that's what you were asking