He will reach here . . . . . . . . sunset. A. in B. for C. at D. on

The other prepositions are not as accurate in this context. The preposition “in” is used to indicate a period of time, but it is not specific enough to indicate the exact time of arrival. The preposition “for” is used to indicate a purpose or reason, but it is not clear what the purpose of the person’s arrival would be. The preposition “on” is used to indicate a day or date, but it is not clear what day or date the person is expected to arrive.

Therefore, the preposition “at” is the most accurate choice in this context.