The temperature at which the readings are the same on Celsius and Fahrenheit thermometers is -40 degrees; option [A]. At this temperature, -40 degrees Celsius is equivalent to -40 degrees Fahrenheit. This unique point, -40°C, is where the two temperature scales intersect, making it the only temperature where the readings on both thermometers are identical. This convergence occurs because the Celsius and Fahrenheit scales have different starting points and intervals, but they intersect at -40°C/-40°F, providing a rare instance of temperature equivalence between the two scales.