Answer: b. "Ambush" talks of a soldier who can't share his feelings with his daughter but hopes to someday, while "Symptoms" deals with soldiers who have lost all memories of the worst experiences of war.
Explanation: The theme differs in the two excerpts because in "Ambush" the narrator talks of a soldier who remembers having killed someone but does not want to share those memories with her daughter at the moment of speech because she is a nine-year-old. He will share his experiences with her when she is a grown-up, though. In "Symptoms" the narrator states that soldiers remember some events but cannot recall their worst experiences.