The use of submarines during world war i had which of these effects? it gave an advantage to the coastal nations.
it made naval battles the key battles of the war.
it made it difficult for merchants to bring supplies to the allies.
it prevented the central powers from transporting troops.

The best and most correct answer among the choices provided by your question is the second choice or letter B.

The use of submarines during World War I had made naval battles the key battles of the war.

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