The correct answer is A) Texas would be admitted as a slave state.
The Republic of Texas existed from 1836 to 1845 before Texas joined the United States. Besides the likelihood of war with México, annexation took so long because Texas would be admitted as a slave state.
After Mexico defeated the Spanish Army in the War of Independence, the government of Mexico supported the idea of accepting foreigners to populate the region. That is when Stephen F. Austin brought some people to inhabit close to the banks of the Brazos River. Then after the war with México, Texas was admitted to the Union as a slave state on December 29, 1845.