Choice C is the best answer. The data in the figure show the greatest below-average temperature variation occurred in 1675 CE, as the temperature reached a variation of −1.0° Celsius.
Choice A is incorrect because the figure shows that the temperature in 1200 CE was above average (+0.25° Celsius). Choices B and D are incorrect because the below-average temperature variation reported in 1675 CE (at −1.0° Celsius) was greater than the below-average temperature variation reported for 1375 CE (around −0.25° Celsius) and 1750 CE (around (−0.5° Celsius).