## **Core Concept**
Gross motor skills in children follow a predictable sequence and are often used as milestones to assess developmental progress. Riding a tricycle and climbing stairs with alternate steps are specific motor skills that indicate a certain level of physical coordination and strength.

## **Why the Correct Answer is Right**
The ability to ride a tricycle is typically achieved around 3 years of age, as it requires balance, coordination, and the ability to pedal with both feet. Climbing stairs with alternate steps, also known as "stepping over" or reciprocal walking up stairs, usually develops around the same age or slightly later. These skills are indicative of a child having reached a developmental age of approximately 3 years, as they reflect advanced gross motor capabilities.

## **Why Each Wrong Option is Incorrect**
- **Option A:** Typically corresponds to a developmental age younger than 3 years, where children might start to show some gross motor skills but not to the extent of riding a tricycle or climbing stairs with alternate steps.
- **Option B:** Could correspond to a slightly younger or older age depending on the specific developmental milestones listed, but generally does not align with the skills described.
- **Option D:** Corresponds to an older developmental age, where children would be expected to have mastered more complex skills than those described.

## **Clinical Pearl / High-Yield Fact**
A key developmental milestone to remember is that by 3 years of age, children should be able to ride a tricycle, show improvement in balance and coordination, and perform actions like climbing stairs with support or independently. Pediatricians often use these milestones to assess if a child is developing at a typical pace.

## **Correct Answer:** . 3 years.