What is the best conclusion that can be drawn from this graph? The correct answer is letter A: Germany was stepping up its efforts to stop goods from reaching the Allies.
As soon as the WW1 started the British navy blockaded all German ports, causing one of Germany defeat ( called Turnip winter 1916-1917, because 'turnip' was almost all that the Germans had to eat). As a consequence, the Germans tried to win the naval war by using U-boats to sink ships that bring supplies to Britain. This was their only hope of winning the war, and they almost succeeded. In Abril 1917 London was reduced to two days' supply food. So the Prime Minister changed his tactics and introduced a 'convoy system' (merchant ships that sailed in large groups escorted by a destroyer), this tactic made it more difficult for U-boats to attack.