If A -> B and not B, what can be concluded about A?

• A. A is true
• B. Not A
• C. B is true
• D. A implies B

Answer: (B)

The idea being tested is modus tollens: if A implies B, and B is false, then A cannot be true. Here A → B and ¬B. If A were true, B would have to be true as well, which contradicts ¬B. Therefore A cannot be true, so A is false. Equivalently, from the contrapositive, if B is false, then A must be false. This is the spot where the conclusion comes from.