(A) The Germans sank British supply boats
(B) The Germans sank American ships
(C) Germany invaded Russia
(D) ** Germany invaded Belgium
EXPLANATIONS BELOW
Concept note-1: -Germany’s invasion of Belgium tipped the balance for Britain. At 2pm on 4 August, it issued an ultimatum demanding Germany withdraw its troops. At 11pm, the deadline passed without a reply. Britain declared war.
Concept note-2: -On September 3, 1939, in response to Hitler’s invasion of Poland, Britain and France, both allies of the overrun nation declare war on Germany.
Concept note-3: -Of course, Belgians refused to let them through, so the Germans decided to enter by force and invaded Belgium on Aug. 4, 1914. By doing so, they violated the Treaty of London, which is why Great Britain, that was bound to guard the neutrality of Belgium, entered the war.
Concept note-4: -After weeks of speculation and mounting tension, Great Britain declared war on Germany on 4 August 1914.