"A" is quite correct, though "C" adds a bit more detail of how soldiers felt about Trench Warfare. In my honest opinion, I think "D" is the correct answer.
Trench Warfare was rather horrific, and brutal to say the least -- it was also "boring" during stalemates if neither party was engaging in any sort of push.
Note: I'm not a teacher of any sorts! This is just my opinion from things I've learned in the previous years.
