Mark the letter A,B,C, or D on your answer sheet to indicate the word or phrase that is CLOSEST in meaning to the underlined part in each of the following questions.
Milk is fortified with vitamin D, and drinking non-fat milk gives you calcium, vitamin and energy. However, if you decide to take supplemental vitamin D, 400 to 800 IU per day will safely prevent any deficiencies.
A.additional
B.special
C.natural
D.concentrate