**Core Concept**
Pseudoparalysis in infants refers to a condition characterized by refusal to move a limb due to pain, despite the absence of any detectable neurological deficits. This condition is often associated with nutritional deficiencies that affect bone growth and development.

**Why the Correct Answer is Right**
Vitamin C deficiency is a well-known cause of pseudoparalysis in infants. This occurs due to impaired collagen synthesis, which affects the growth and development of bones and joints. Vitamin C is essential for the incorporation of hydroxyproline and hydroxylysine into collagen, and its deficiency leads to fragile bones and joints, causing pain and discomfort. As a result, infants may refuse to move a limb to avoid exacerbating the pain. The condition is often referred to as scurvy.

**Why Each Wrong Option is Incorrect**
* **Option A:** Acute Rheumatic fever can cause joint pain and stiffness, but it does not typically present with pseudoparalysis in infants.
* **Option B:** Vitamin B6 deficiency can cause neurological symptoms, but it is not associated with pseudoparalysis in infants.
* **Option C:** Vitamin E deficiency can cause neurological symptoms and weakness, but it is not typically associated with pseudoparalysis in infants.

**Clinical Pearl / High-Yield Fact**
Scurvy due to vitamin C deficiency can be prevented by ensuring adequate vitamin C intake through a balanced diet or supplements. Breastfed infants of mothers with limited vitamin C intake may be at higher risk of scurvy.

**✓ Correct Answer: D. Vitamin C deficiency**