Why did the Allies attack the Ottomans on the Gallipoli Peninsula in 1915?

a The Allies wanted to punish the Ottomans for the Armenian genocide.
b The Allies had hoped to supply Russia by way of a southern sea route.
c The Ottomans had recently switched sides by fighting with the Austrians.
d The Ottomans pledged to send troops to support the Germans on the Western Front.