Let A=[1,5]A = [1, 5]A=[1,5] and B=[3,7]B = [3, 7]B=[3,7] be intervals on the real number line. What is their union A∪BA \cup BA∪B?
[3,5][3, 5][3,5]
[1,7][1, 7][1,7]
[1,3][1, 3][1,3]
[5,7][5, 7][5,7]