**Core Concept:** Vitamin A is an essential micronutrient required for various physiological processes, including vision, immune function, and cell differentiation. Infants depend on the maternal stores or breast milk for their vitamin A requirements. Retinol is the biologically active form of vitamin A.

**Why the Correct Answer is Right:** The recommended dietary allowance (RDA) for Vitamin A in infants refers to the minimum daily amount needed to maintain optimal health. In infants, breast milk already provides adequate retinol to meet their needs. Consequently, the correct answer is 'D', indicating that the RDA for Vitamin A in infant is "not applicable".

**Why Each Wrong Option is Incorrect:**

A. This option is incorrect because Vitamin A is present in breast milk and does not need to be supplemented in infants receiving exclusive breastfeeding.
B. This option is incorrect as infants' needs are met through breast milk or maternal stores.
C. This option is incorrect because infants do not require Vitamin A supplementation, as mentioned above.

**Clinical Pearl / High-Yield Fact:**

Breast milk contains retinol and beta-carotene, which is efficiently converted to retinol in the infant's gut. Vitamin A supplementation is not recommended unless there are specific deficiencies or risk factors present. Understanding the vitamin A needs in infants aids in preventing unnecessary exposures to potentially harmful substances, ensuring optimal infant health.