Trench warfare began after germany failed in its initial plan to a seize france and bring a quick end to the war. b negotiate a temporary truce with the allied forces. c attack the allies by sea with its powerful navy. d storm across the eastern front to attack russia.

Trench warfare began after Germany failed in its initial plan to A. seize France and bring a quick end to the war. 
Germany didn't really have any desire to attain a truce with the Allies because it wanted to win immediately; it didn't have a powerful navy so that one's incorrect as well; D is incorrect because it wasn't their plan at the time. After it failed to conquer France, Germany decided to begin the trench warfare.