Which logic gate outputs true if at least one input is true?

• A. AND gate
• B. NOT gate
• C. NOR gate
• D. OR gate

Answer: (D)

Understanding how basic logic gates respond to inputs. When at least one input is true, the gate that outputs true is the OR gate. An OR gate outputs true if any input is true; with two inputs, if either input is true, the output is true, and the only time it’s false is when all inputs are false. The same idea holds for more inputs: as soon as any input is true, the output becomes true.

This differs from the AND gate, which requires every input to be true to produce a true output. The NOT gate inverts its single input, so it doesn’t apply to the “at least one input is true” situation. The NOR gate outputs true only when all inputs are false, which is the opposite of the described condition.

Therefore, the gate that matches “true if at least one input is true” is the OR gate.