When Rianna was 11 months old, she was injured in a car crash. She was in a coma for almost a year and then spent many months of recovery from a brain injury. By her third birthday, although she is making good process, she has not yet spoken, and her parents are fearful that she will never speak. The doctors, however, feel confident that Rianna will learn to speak. This is because the first four years are not a for language learning.

This is because the first four years are not a critical period for language learning

Explanation:

According to the Critical Period Hypothesis (CPH) which states that the first few years of life constitute the time during which language develops and after which sometime between age 5 and puberty language learning becomes much more difficult and ultimately less successful.

Since Rianna just turned 3, she has not reached the critical period for language learning and can still learn how to speak.