Concept:When parts of the day are used in a general sense, they do not take the article "the".Explanation:The expression refers to the whole period of daylight in a general way, not to one specific morning or evening.So both "morning" and "evening" should be used without "the".Options A, B, and C unnecessarily add "the", which makes them ungrammatical or unidiomatic.Therefore, the idiomatic completion is "morning till evening".Answer:D. morning till evening