Final answer:
Bernetta's autoimmune disease affects her salivary glands, leading to trouble swallowing.
Step-by-step explanation:
Bernetta's autoimmune disease that affects her salivary glands might be causing them to break down and become non-functional. This could be due to the immune system producing antibodies against her own proteins present in the salivary glands. As a result, Bernetta may have trouble swallowing, which is option D in the question.