Fact 1: All hats have brims. Fact 2: There are black hats and blue hats. Fact 3: Baseball caps are hats.
If the first three statements are facts, which of the following statements must also be a fact? I. All caps have brims. II. Some baseball caps are blue. III. Baseball caps have no brims.
I. I only
II. II only
III. I, II, and III
IV. None of the statements is a known fact.

Question: 以下哪项是正确的？
Options:
A. 非 I, B. IV 或 III, C. II 或 I, D. IV 或 I, E. 仅 II
Answer: A
B
D
True statement: IV