I think the best answer is C: "Use of chemical agents in warfare would be undesirable."
The passage doesn't really support option A or B. It's not talking about civil strife, and it's not saying chemical agents are actually useful.
Option D goes too far - it says ALL people in the military like chemical weapons, which isn't what the passage says.
The passage seems pretty negative about chemical weapons overall. It uses words like "regretfully" when talking about people who support them. It also describes modern warfare as "suppression of civilian populations," which sounds bad.
The author is basically saying "Some military people think chemical weapons are useful for modern warfare", and that's regretful. So C fits best - it's capturing that chemical weapons in war would be a bad thing, which seems to be the main point the author is making.
It's not a perfect option either, but it's the closest of the options given. the overall tone of the passage fits option C best.