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You insert a special “question card” into the machine. The card has a question written on it, plus three possible answers . . . these are labeled “A,” “B,” and “C.” Your friend reads the question and then touches the “answer stick” to one of the three “answer bars.” If he has chosen the correct answer, the corresponding “answer light” lights up. If not, the light remains out. The secret of the machine’s operation can be found at the bottom of the specially prepared question card. Notice the small piece of aluminum foil. Besides presenting a question, the card serves as a switch “element” that controls the answer lights. Here’s how: The question card slips into a trio of switch contact pairs . . . each of which is wired in series with one of the answer lights (look at the diagrams if you find any of this confusing). You must decide in advance which answer . . . “A,” “B,” or “C” . . . will be the correct answer. Then, you prepare the card by cementing a piece of aluminum foil to the card’s bottom edge, at the corresponding location.