Answer:
B. In the first half, the speaker describes a gas attack; in the second half the speaker uses the event to try to convince readers that war should not be glorified
Step-by-step explanation:
"Dulce et Decorum Est" describes the horrors experienced by soldiers in the first world war, the most bloody and impactful that had been carried out at that time. The author shows how war is not beneficial, but sad, dirty and evil.
In the first part of the poem, he describes the battles themselves, showing a moment when a gas attack caused many problems. He continues the poem showing how harmful war is and that it should not be justified, glorified and encouraged, by anyone.