Which device outputs true only when both inputs are true?

• A. OR gate
• B. NAND gate
• C. XOR gate
• D. AND gate

Answer: (D)

The main idea is that this device performs a logical conjunction: the output is true only when both inputs are true. An AND gate follows the rule that all conditions must be satisfied for the result to be true. If both inputs are true, the output is true; in every other case (true with false, false with true, or both false), the output is false. This is why it matches the description “outputs true only when both inputs are true.”

To see why the others don’t fit: an OR gate would be true if either input is true, so it can be true when only one input is true. an XOR gate is true when exactly one input is true, not both. a NAND gate is the opposite of AND, giving false only when both inputs are true. So only the AND gate satisfies the condition.