Final answer:
The correct diagram will depict the Northern Hemisphere tilted away from the Sun and the Southern Hemisphere tilted towards the Sun, in line with Earth's 23.5° axial tilt during December.
Step-by-step explanation:
The diagram that best represents the tilt of Earth's axis in December would show the Northern Hemisphere leaning away from the Sun and the Southern Hemisphere leaning towards the Sun. This is due to Earth's tilt of 23.5° and its position in its orbit around the Sun during December, which corresponds with the winter solstice in the Northern Hemisphere. On December 21st, for example, the North Pole experiences 24 hours of darkness while the South Pole is illuminated, a phenomenon shown in Figure 4.9. This positioning results in the Sun being at the zenith for observers on the Tropic of Capricorn and indicates that the Sun's rays will be striking the Northern Hemisphere at a low angle, making the Sun appear low in the sky.