Stop the use of this Venn diagram in school as it is not fully functional and does not have a category for A and C or B and D:

Not fully functional Venn diagram

Use this one instead as it has a category for every combination of A, B, C, and D:

Fully functional Venn diagram

The fists Venn diagram is used too often in schools and is not fully functional, the second one should be used instead.