Remark
Some of these statements are true, but they are not mentioned. Watch out for that possibility.
Discussion
I don't see anything about an inability to carry out their duties during war. The problem in both cases is that they did carry out their responsibilities and duties all too well. A is incorrect.
B: It isn't B. It isn't the physical problems that give the trouble. It is the mental problems that cause trouble -- especially the flashbacks for O'Brien and the lack of memory for Steinbeck's soldiers.
C: I don't think you could say anything but C, especially in O'Brien's case. That's your answer.
D: O'Brien certainly didn't hate his enemy. He regretted that he did what he was forced to do. He realized he cut off the hopes and dreams of another human being. Not an easy thing to live with.
