Question

this is your code.

>> a = 5, 10, 15

>> b = 2, 4, 6

>> c = dog, cat, bird

>> d = a, b, c

how do you refer to 15?

Explanation:

Step1: Analyze list structure

The variable d is a list of lists where d = [a, b, c], a = [5, 10, 15], b = [2, 4, 6], c = ['dog', 'cat', 'bird'].

Step2: Locate element 15

The element 15 is in list a. In Python, list indices start from 0. So a is the first element of d (index 0) and 15 is the third - element of a (index 2).

Answer:

d[0][2]