Respuesta :
The U-boats attacked not only by enemy ships but also by commercial supply ships during the year 1915 and 1917.
Option D is correct.
What were the U-boats?
The U-boats were the submarines used by the country of Germany in both the world wars.
In the year 1915 and the 1917, the enemy ships and the commercial ships were attacked the U-boats which are being called in current times as Type 12.
Therefore, the correct option is option D.
Learn more about the U-boats in the related link:
https://brainly.com/question/18187346
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