If A = {1, 2, 3, 4} and B = {4, 5, 6, 7} then A∪B should be

• A. {2, 3, 4, 5, 6, 7}
• B. {1, 2, 3, 4, 5, 6, 7}
• C. {4}
• D. {1, 2, 3, 5, 6, 7}