What were three reasons that the German government restored to submarines warfare?

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. A string of attacks on merchant ships followed, culminating in the sinking of the British ship Lusitania by a German U-boat on May 7, 1915. Although the Lusitania was a British ship and it was carrying a supply of munitions—Germany used these two facts to justify the attack—it was principally a passenger ship, and the 1,201 people who drowned in its sinking included 128 Americans. The incident prompted U.S. President Woodrow Wilson to send a strongly worded note to the German government demanding an end to German attacks against unarmed merchant ships. 

a peace conference held after the surrender of japan

an international conference held near the end of world war ii

a meeting of the victorious nations after the defeat of germany

a summit meeting between the united states and the soviet union

b: to eliminate competition from other farmers