What Was the Public Motive for Britain's Declaration of War

Multiple Choice

What was the public motive for Britain's declaration of war in 1914?

A) The Austro-Hungarian attack on Serbia.
B) The threat posed by German submarines to the world's shipping lanes.
C) The German declaration of war on France;that activated the Anglo-French alliance.
D) The German invasion of neutral Belgium.
E) The Russian declaration of war on Germany,which required Britain to declare war by treaty.