The correct option is A at 8 o'clock on
Prepositions express a relation (of things like place and time) between the noun and the rest of the sentence.
Option A: This option is incorrect because there is no relation expressed between the noun that expresses time '8 o'clock' and the sentence.
Option B: This option is incorrect because it doesn't have any preposition that expresses the relation between the time '8 o'clock' as well as the day 'Sunday', with respect to the action 'start'.
Option C: This option is incorrect because it does not have a preposition that connects the words '8 o'clock' and 'Sunday'. As a result, there isn't any relation formed between these nouns.
Option D: This is the most appropriate option, as it expresses the relation of time 'at 8 o'clock' and 'on' with respect to the day 'Sunday'.