A nurse is reinforcing teaching to a group of parents about potential causes of autism spectrum disorder (ASD). Which of the following statements should the nurse reinforce?

A. "Vaccinations, especially the MMR vaccine, have been proven to be a leading cause of autism in children." This statement is false. Extensive research has shown no link between vaccines, including the MMR vaccine, and autism. The original study suggesting a connection was discredited and retracted due to fraudulent data. B. "ASD is primarily caused by poor parenting and a lack of nurturing in early childhood." This outdated theory, once known as the "refrigerator mother" hypothesis, has been debunked. Autism is a neurodevelopmental disorder with biological origins, not a result of parenting style. C. "The exact causes of autism spectrum disorder are not fully understood, but it is believed to be related to a combination of genetic and environmental factors." This is correct. Research suggests that genetic predisposition, along with environmental influences (such as prenatal factors or advanced parental age), plays a role in ASD development. However, no single cause has been identified. D. "ASD can be caused by consuming gluten and casein, which are found in wheat and dairy products, respectively." There is no scientific evidence that gluten or casein causes autism. While some parents report behavioral improvements on gluten-free or casein-free diets, these diets do not cause or cure autism.