(A) ** Germany’s policy to sink any ship in British waters without warning
(B) the U.S. Navy’s warning of the type of warfare the Central Powers could expect
(C) Germany’s decision to focus its resources on the waters surrounding Europe
(D) Britain’s policy to sink any ship in German waters without warning
EXPLANATIONS BELOW
Concept note-1: -Unrestricted submarine warfare was first introduced in World War I in early 1915, when Germany declared the area around the British Isles a war zone, in which all merchant ships, including those from neutral countries, would be attacked by the German navy.
Concept note-2: -Germany’s resumption of submarine attacks on passenger and merchant ships in 1917 was the primary motivation behind Wilson’s decision to lead the United States into World War I.
Concept note-3: -RMS Lusitania was torpedoed by a German U-boat on 7 May 1915.