Final answer:
To create the illusion of a burning candle in a mirror, place a real burning candle behind the unlit one in such a way that the mirror reflects the hidden flame's light onto the unlit candle, making it appear to be alight.
Step-by-step explanation:
To make an unlit candle appear as if it is burning in a mirror reflection, you would select option B: By using a real burning candle behind it. When the real candle is strategically placed behind the unlit candle, and the flame is hidden from direct view, the mirror can reflect the flame's light, giving the illusion that the unlit candle in front is actually burning. This is a simple yet effective optical illusion utilizing the principles of light reflection. Remember to observe safety precautions when handling real flames to prevent accidents. This method is much more effective than simply shining a flashlight on it (option C) or placing a glowing LED near it (option D), which would not convincingly mimic the natural glow and flicker of a candle flame.