learning task 3:
2. A n C=
3. B'=
4. A-E=
5. C U E.

2. (2, 3, 5)
3. (6, 7, 8, 9, 10)
4. (1, 3, 5)
5. (2, 3, 5, 7, 2, 4, 6, 8, 10)