20. Of the following, which has Earth completed when it makes one revolution around the Sun?
Answer: A
One Earth year
Earth completes one full revolution around the Sun in the span of one Earth year, which is defined as the time it takes for the planet to orbit the Sun once.
A) One Earth year
This option is correct because it directly describes the duration of time it takes for Earth to complete one full orbit around the Sun, which is exactly one Earth year or approximately 365.25 days.
B) One Earth day
This option is incorrect as one Earth day refers to the time it takes for Earth to complete one full rotation on its axis, which is approximately 24 hours, not a revolution around the Sun.
C) One light year
This option is incorrect because a light year is a measure of distance, specifically the distance that light travels in one year, not a measure of time related to Earth's orbit around the Sun.
D) One lunar month
This option is incorrect because a lunar month refers to the time it takes for the Moon to complete its phases, which is about 29.5 days, and does not relate to the duration of Earth's revolution around the Sun.
Conclusion
The correct answer is A) One Earth year because it accurately captures the time frame for Earth’s revolution around the Sun. All other options are either measures of time unrelated to the Earth's orbit or describe different celestial phenomena. Thus, option A stands out as the only accurate representation of Earth's annual orbital cycle.