Here are the answers to your questions:
Question 1: What was the “root issue” that prevented Congress from adding Texas to the U.S. for many years?
Answer: B - the issue of slavery
Question 2: Which of these Presidents was MOST responsible for making Texas a state?
Answer: C - Tyler
Question 3: The Mexican War effectively ended with the capture of __________.
Answer: D - Mexico City
Question 4: Which of these was part of the Treaty of Guadalupe Hidalgo?
Answer: B - US paid Mexico $15 million.