Final answer:
Soldiers dug trenches to protect themselves from artillery shells, snipers, and mustard gas during World War I.
Step-by-step explanation:
Trenches were dug by soldiers fighting on the front lines as a defensive measure during World War I. The threat of artillery shells, snipers, and mustard gas forced soldiers to take cover in trenches to protect themselves from enemy attacks. Trenches provided soldiers with a safe space to take refuge and reduce the risk of being directly hit by weapons or chemical agents.
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