Given X = {numbers divisible by 2 which are less than or equal to 1} and Y = {multiples of 3 that are less than 18}, what is X ∪ Y?

a. {6} b. {3,6,9,12,15} c. {2,4,6,8,10} d. {2,3,4,6,8,9,10,12,15}