Final answer:
The statement made by the parent that indicates understanding of the teaching is 'The onset of autism usually occurs before 3 years of age.'
Step-by-step explanation:
The statement made by the parent that indicates understanding of the teaching is b. 'The onset of autism usually occurs before 3 years of age.' This statement is correct because autism spectrum disorders typically present in early childhood, with symptoms and challenges becoming evident before the age of 3. It is important for parents and healthcare providers to recognize the early signs of autism to facilitate early intervention and support.