**Core Concept**
The question is testing the understanding of **developmental milestones** in infants, specifically the age at which certain physical and cognitive abilities are achieved. The ability to follow an object with 180 degrees of motion, hold the neck up, and sit with or without support are key indicators of a baby's neurological and muscular development.

**Why the Correct Answer is Right**
The correct answer corresponds to an age where a baby can track moving objects over a wide range, indicating good **cervical control** and beginning **visual tracking** skills. Holding the neck up suggests sufficient strength in the **neck muscles**. Sitting with support but not without indicates the baby is developing **trunk control** but may not yet have the balance or strength to sit unassisted.

**Why Each Wrong Option is Incorrect**
**Option A:** This age is typically too early for the described abilities.
**Option B:** This age might be slightly early for consistent sitting with support.
**Option D:** This age is too late, as most babies can sit without support by this time.

**Clinical Pearl / High-Yield Fact**
A key point to remember is that by around 6-7 months, most babies should be able to sit without support, which is a crucial **developmental milestone**.

**Correct Answer:** C. 6 months