D-day

英 ['di:-dei] 美

D-day (n.): 1918, "date set for the beginning of a military operation," with D as an abbreviation of day; compare H-hour, also from the same military order of Sept. 7, 1918:
The First Army will attack at H-Hour on D-Day with the object of forcing the evacuation of the St. Mihiel salient. [Field Order No. 8, First Army, A.E.F.]
"They designate the day and hour of the operation when the day and hour have not yet been determined, or where secrecy is essential" [U.S. Army Center of Military History Web site]. Now almost exclusively of June 6, 1944.

1. Butter, margarine, and oily fish are all good sources of vitamin D.: 黄油、人造黄油和多脂鱼都含有丰富的维生素D。

2. In figure 24 "D" denotes quantity demanded and "S" denotes quantity supplied.: 在图24中，D代表需求量而S代表供应量。

4. This special form of vitamin D is naturally present in breast milk.: 这种特殊形态的维生素D天然存在于母乳中。