Research suggests that bilingualism has a negative effect on: A. Ianguage development. B. cognitive development. C. metalinguistic awareness. D. none of the above.

First, make sure to read and understand the question properly. The question asks about the negative effects of bilingualism, so pay attention to the listed options and think about whether each option could be a negative effect or not.

Now, consider each of the given options one by one: A - Language development: Studies have shown that bilingualism does not have a negative impact on language development. In fact, it has been found to enhance language learning abilities in individuals. B - Cognitive development: There is no evidence to suggest that bilingualism has a negative impact on cognitive development. Rather, numerous studies have evidenced that bilingualism can positively affect cognitive functions like executive control, attention, and working memory. C - Metalinguistic awareness: Metalinguistic awareness refers to the ability to think and talk about language. Studies have demonstrated that bilinguals have greater metalinguistic awareness compared to monolinguals, as managing two languages offers more opportunities to reflect on the structure and use of language. Considering all of the points mentioned above, none of the given options A, B, and C indicate a negative effect of bilingualism.

Based on the information provided, the correct answer is: D - None of the above.