The dynamic-set operation UNION\text{UNION}UNION takes two disjoint sets S1S_1S1​ and S2S_2S2​ as input, and it returns a set S=S1∪S2S = S_1 \cup S_2S=S1​∪S2​ consisting of all the elements of S1S_1S1​ and S2S_2S2​. The sets S1S_1S1​ and S2S_2S2​ are usually destroyed by the operation. Show how to support UNION\text{UNION}UNION in O(1)O(1)O(1) time using a suitable list data structure.

In the context of the box model, what is the difference between a margin and a padding? a. a padding lies outside a box border, while a margin lies inside it. b. a padding lies inside a box border, while a margin lies outside it. c. a padding can be adjusted independently, while a margin depends on the size of its box. d. a padding depends on the size of its box, while a margin can be adjusted independently.