Fact 1: Mary said, "Ann and I both have cats."
Fact 2: Ann said, "I don't have a cat."
Fact 3: Mary always tells the truth, but Ann sometimes lies.

If the first three statements are facts, which of the following statements must also be a fact?
I: Ann has a cat.
II: Mary has a cat.
III: Ann is lying.

Explanation:-

If Mary always tells the truth, then both Ann and Mary have cats (statements I and II), and Ann is lying (statement III). So all the statements are facts.