The correct answer is: D. None of the above
The length of the day is determined by the Earth’s rotation on its axis. It takes the Earth 23 hours, 56 minutes, and 4.09 seconds to rotate once on its axis. This is called a sidereal day. A solar day is the time it takes for the Sun to return to the same position in the sky, as seen from Earth. It is slightly longer than a sidereal day, at 24 hours.
Astronomical units are a unit of length used to measure the distance between astronomical objects. One astronomical unit is equal to the average distance between the Earth and the Sun, which is about 150 million kilometers.
Solar terms are a system of dividing the year into 24 periods, each of which is about 15 days long. The solar terms are based on the Sun’s position in the sky, and they are used to track the seasons.
The length of the hours is a human-made construct. It is based on the Earth’s rotation on its axis, but it is not a perfect measure of that rotation. The Earth’s rotation is slowing down very gradually, so the length of the hour is also slowly getting longer.