Tested on video using the sample "0" question number. The correct answer is D, which causes the green light and buzzer to sound, I then chose C which is wrong and made the red light and buzzer to sound.  It's in pretty nice condition, made in 1978, "partial assembly in USA using certain components of foreign origin". Do you remember your 1970's trivia? Takes a 9V battery, not included per USPS policy.  Includes cartridge/quiz book #1, subsequent cartridges/quiz books are available on ebay.