To solve this question, the user needs to know the correct verb tense to use when describing the action of the sun. The verb tense should indicate that the action occurred in the past.
Option A: "sat" is the past tense of "sit" and is not the correct verb to use in this context.
Option B: "set" is the correct past tense of "set" which means to go below the horizon. Therefore, this option is correct.
Option C: "setted" is not a correct past tense of "set".
Option D: "was setting" is the past continuous tense of "set" and does not correctly indicate that the action was completed in the past.