Describe the universal set

Answer:
The correct answer is the first option: "Universal set = set of numbers from 0 to 20."
Step-by-step explanation:
The universal set (U ) is the set of all elements under consideration:
U = {0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 10, 20}
B = {2, 4, 6, 8, 10, 12, 14, 16, 18, 20}
C = {1, 3, 5, 7, 9, 10, 11, 13, 15, 17, 19, 20}
Basically everything inside the rectangle, including the zero outside the venn diagram, are included in the universal set.