Between 1915 and 1917, how did the strategies the Germans used at sea differ from those of the Allied Powers?

A). Germany attacked non-military ships and those of the US, a country not involved in the war.
B). Germany refused to stop their attacks despite complaints from the US and other neutral countries.
C). Germany included the use of submarines in the types of boats used to attack enemy ships.
D). Germany used their submarines and other military ships for both commercial and military purposes.