I just read about this! Let's go through them together. Option A is clearly not even close to the answer because the Trenches were cold, muddy, and traumatizing for soldiers at the time. Option B is reasonable and serves as the whole purpose of trenches in the first place, however, it did not protect soldiers from diseases. Option C has a reasonable explanation to the reality of trenches and the results of diseases and infections that occurred within the horrid living conditions. Option D is not correct because trenches did not change it from a two-front war to a one-front war; in fact it worsened that aspect.
The answer is C. :)
