Final answer:
Saeng and her parents primarily communicate non-verbally through the use of gestures. She learned signs but did not become fluent in spoken language, though she can understand basic responses like 'yes' and 'no.'
Step-by-step explanation:
According to the information provided, Saeng and her parents generally communicate with each other non-verbally. This is evidenced by her ability to learn signs and use gestures, even though she never fully mastered verbal language. While she can understand and use simple responses such as "yes" and "no", the primary mode of communication between Saeng and her parents is likely through non-verbal means, specifically through the use of gestures. Hence, the answer to how Saeng and her parents generally communicate with each other is D) Non-verbally through gestures.