Concept: The earth's revolution refers to the orbital movement of the earth around the sun along its fixed path.
Explanation: The earth takes about
36541 days to complete one full revolution around the sun.
This fixed time period is measured as one solar year.
Hence, the earth's revolution directly determines the length of a year.
Day and night, dawn and twilight, and apparent sunrise and sunset are all effects of the earth's daily rotation on its axis, not its revolution.
Therefore, among the options listed, the determination of a year is the only correct effect of the earth's revolution.
Answer: B. It determines a year