The correct answer is: D. Winter solstice.
The winter solstice is the shortest day of the year in the Northern Hemisphere. It occurs on December 21 or 22, and marks the beginning of winter. After the winter solstice, the days begin to get longer and the nights shorter.
The spring equinox occurs on March 20 or 21, and marks the beginning of spring. The summer solstice occurs on June 20 or 21, and marks the beginning of summer. The autumn equinox occurs on September 22 or 23, and marks the beginning of autumn.
On the winter solstice, the Northern Hemisphere is tilted away from the sun, which means that the sun’s rays strike the Earth at a lower angle. This results in shorter days and longer nights. After the winter solstice, the Northern Hemisphere begins to tilt towards the sun, which means that the sun’s rays strike the Earth at a higher angle. This results in longer days and shorter nights.