The python program has four lists, A, B, C, and E which is a list of the first three lists. Lists are unordered indexed data structures, it is accessed by an index starting from 0 to n (which is the length of the list minus one).
The E list is a list of lists with three list items starting from index zero to two. E[0][1] is used to access the item "dog" in the first list item of the E list.
