**Core Concept**
Language development in children is a complex process that involves significant cognitive, social, and neurological changes. The ability to use words with meaning is a critical milestone in language acquisition, reflecting the maturation of the left hemisphere of the brain, particularly the Broca's area and Wernicke's area. This process is influenced by genetic, environmental, and socio-cultural factors.

**Why the Correct Answer is Right**
The correct answer is based on the concept of language development stages, as described by Jean Piaget and later refined by others. Typically, a child starts using single words around 12-18 months of age, followed by two-word combinations around 18-24 months, and eventually develops the ability to use short sentences and around 10 words with meaning by 24-30 months of age. This corresponds to the preoperational stage of cognitive development, where children begin to use language to communicate more effectively.

**Why Each Wrong Option is Incorrect**
* **Option A:** This option is likely too early, as most children do not start using words with meaning until around 18-24 months of age.
* **Option B:** This option is too vague, as it does not provide a specific age range or developmental stage.
* **Option C:** This option is too late, as most children have already developed the ability to use 10 words with meaning by 30 months of age.

**Clinical Pearl / High-Yield Fact**
The critical period for language acquisition is between birth and 7 years of age, during which the brain is most malleable and receptive to language learning. After this period, language acquisition becomes increasingly difficult and may require more effort and practice.

**Correct Answer: D. 2 years.**