Final answer:
The most appropriate action is to allow the patient to cry.
Step-by-step explanation:
In this situation, the most appropriate action for the medical assistant is to allow the patient to cry. Expressing emotions, such as crying, can be a natural response to a terminal diagnosis, and it is important for the patient to be able to process their feelings. By allowing the patient to cry, the medical assistant creates a supportive and empathetic environment. This can help the patient feel more understood and may lead to better emotional well-being and coping.