Suppose that some knowledge base contains various propositional-logic sentences that utilize symbols A, B, C, D (connected with various connectives). There are only two cases when the knowledge base is false:

- First case: when A is true, B is true, C is true, D is true.

- Second case: when A is true, B is false, C is true, D is false.

In all other cases, the knowledge base is true.

Write a conjunctive normal form (CNF) for the knowledge base.