FINAL ANSWER:
D. U-boat attacks
Step-by-step explanation:
The term "doughboy" is commonly used to refer to the American soldiers who fought on the Western Front during World War I. The Western Front was primarily in Europe, and it was known for the intense trench warfare and battles between the Allied and Central Powers.
U-boat attacks, on the other hand, were primarily associated with naval warfare and occurred in the Atlantic Ocean. U-boats were German submarines that targeted Allied ships, including civilian vessels, during World War I. Doughboys, as infantry soldiers, were not directly involved in naval warfare or U-boat attacks. Therefore, option D, "U-boat attacks," was not a part of the typical doughboy's experience on the Western Front.