What contributes to variability in syntactic development in bilingual children?

The correct choice is the length of exposure to each language. A child's bilingual development can be significantly influenced by how much time they spend using and being immersed in each language. This exposure is critical, as it provides opportunities for practice and reinforcement of grammatical structures in both languages.

In a bilingual environment, children often receive varying amounts of input and interaction in each language depending on their home, school, and community settings. If a child is exposed to one language more frequently, they may exhibit stronger syntactic skills in that language compared to the other. Furthermore, the nature and amount of exposure—quality interactions, engagement in conversations, and opportunities for reading—can also play a crucial role in the development of syntax.

Other factors listed, such as the influence of cultural context, can affect language use and perception but typically do not direct syntactic development in the same concrete manner as exposure. Similarly, underlying deficits in one language may influence overall communication skills, but they do not specifically address the variability in syntactic development directly tied to bilingual exposure. The quality of early education is essential, but it is often intertwined with and influenced by the amount of exposure a child has to both languages.