Why Did the United States Decline to Annex Texas in 1837

Why did the United States decline to annex Texas in 1837?

A) President Van Buren feared that annexation would spark an American civil war over the issue of slavery.
B) Texans refused to legalize slavery,which was the only condition on which southern politicians would accept Texan statehood.
C) President Van Buren could not convince the Whig-dominated Senate to accept the treaty.
D) The U.S.Congress refused annexation because it did not want to assume Texas's large Mexican population.