Question

during 1915 and 1917, u-boats attacked not only enemy ships but also
troops stationed close to shore.
cities near the shoreline.
german submarines.
commercial supply ships.

Explanation:

During World War I, German U-boats employed unrestricted submarine warfare between 1915 and 1917, targeting enemy military ships and neutral commercial supply vessels carrying war materials to Allied nations, to disrupt Allied supply lines.

Answer:

D. commercial supply ships.