**Core Concept**
The question tests the understanding of neurological reflexes in infants, specifically the Moro's reflex and palmar grasp reflex, and their relationship to the nervous system. These reflexes are crucial in assessing the integrity of the **central nervous system** and **peripheral nervous system** in newborns.

**Why the Correct Answer is Right**
A unilateral Moro's reflex suggests a lesion affecting the **brain** or **spinal cord** on one side, as this reflex is mediated by the **central nervous system**. The presence of a positive palmar grasp reflex indicates intact **lower motor neurons** and **peripheral nerves**.

**Why Each Wrong Option is Incorrect**
**Option A:** This would not explain the unilateral nature of the Moro's reflex.
**Option B:** This is not directly related to the reflexes mentioned.
**Option C:** This option does not account for the unilateral presentation.
**Option D:** This is too general and does not specify the site of the lesion.

**Clinical Pearl / High-Yield Fact**
In clinical practice, assessing reflexes in infants is critical for diagnosing neurological conditions. The Moro's reflex, in particular, is a key indicator of **central nervous system integrity**.

**Correct Answer:** D. Brain or Spinal cord on the affected side.