## **Core Concept**
The core concept being tested here is the immunology of newborns, specifically the normal percentage of CD4+ T cells (also known as T-helper cells) in their total lymphocyte count. CD4+ T cells play a crucial role in the immune system by assisting in the activation and direction of other immune cells.

## **Why the Correct Answer is Right**
In newborns, the immune system is still maturing. A normal newborn has a relatively high percentage of CD4+ T cells compared to adults. Typically, newborns have a higher proportion of CD4+ T cells, which usually ranges around 30-50% of their total T cells, but when considering the total lymphocyte count, the percentage is generally around **30-40%** of lymphocytes being CD4+. This reflects the maturational stage of their immune system.

## **Why Each Wrong Option is Incorrect**
- **Option A:** If the percentage is significantly lower than expected, it might indicate an issue with the newborn's immune system, such as an infection or immunodeficiency. However, without specific numbers, we can't directly refute this option, but given typical values, it's less likely.
- **Option B:** This option might seem plausible but typically, the range for normal CD4+ T cells in newborns as a percentage of total lymphocytes would not usually be cited as this value.
- **Option D:** If this option suggests a significantly higher or lower percentage than expected for newborns, it would be incorrect based on the known ranges for CD4+ T cells in this population.

## **Clinical Pearl / High-Yield Fact**
A key point to remember is that the CD4+ T cell count in newborns is relatively high but decreases with age. Clinicians often monitor CD4+ T cell counts in infants, especially those exposed to HIV, as a critical marker for their immune status and potential need for antiretroviral therapy.

## **Correct Answer:** C. 30-40%