**Core Concept:** Motor development in children, specifically the development of grasping and releasing abilities.

**Why the Correct Answer is Right:** The correct answer, option C, refers to the developmental milestone of a child being able to wring their hands or arms side to side, typically referred to as the "bye-bye" gesture. This skill, also known as "waving," is a significant milestone in a child's motor development and is usually achieved around the age of 8-10 months. The child learns to release their arm and then quickly grasp it again, demonstrating the ability to grasp and release objects.

**Why Each Wrong Option is Incorrect:**

A. Option A is too early, suggesting that children can perform this skill at 3-4 months, which is not accurate as the skill is usually acquired later than 8-10 months.
B. Option B is too late, implying that children should be able to perform this skill by 18 months, which is not the typical age for this milestone.
D. Option D is too vague, referring to a milestone without specifying the age range, which is not helpful when comparing it with the correct answer.

**Clinical Pearl:** Motor milestones, such as waving "bye-bye," provide valuable information about a child's overall development. If a child fails to achieve these milestones within the expected age range, it could indicate developmental delays and prompt further evaluation by a pediatrician or developmental pediatrician.

**Correct Answer:** C. 8-10 months.