## **Core Concept**
Speech development in children is a critical milestone that reflects their neurological and cognitive growth. By a certain age, most children's speech becomes intelligible to strangers, indicating a significant advancement in their communication skills. Understanding the typical age range for this milestone is essential for pediatricians and caregivers to monitor developmental progress.

## **Why the Correct Answer is Right**
By the age of **3 years**, most children's speech is largely intelligible to strangers. At this stage, children typically have a vocabulary of around 1,000 words and start combining two to three words to form simple sentences. Their pronunciation of words becomes more accurate, and they begin to use short sentences, making their speech more understandable to people outside their immediate family.

## **Why Each Wrong Option is Incorrect**
- **Option A:** Speech intelligibility to strangers at **1 year** is generally low because children's vocabulary is limited to a few words, and their pronunciation is often unclear.
- **Option B:** By **2 years**, children start to put two words together and have a vocabulary of around 50 words, but their speech is still not largely intelligible to strangers due to limited vocabulary and pronunciation issues.
- **Option D:** At **4 years**, children's speech is expected to be even more intelligible than at 3 years, with more complex sentences and a larger vocabulary, making this option less specific as the age when "most of the speech is intelligible."

## **Clinical Pearl / High-Yield Fact**
A useful clinical pearl is that by **3 years**, a child's speech should be about 75-80% intelligible to strangers. Significant delays in speech intelligibility can be an early indicator of developmental disorders, and pediatricians often screen for these during routine check-ups.

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