Refer to the passage.

"All the scientific resources of Germany have apparently been brought into play to produce a gas of so virulent and poisonous a nature that any human being brought into contact with it is first paralyzed and then meets with a lingering and agonizing death.”

Sir John French, commander in chief of the British Expeditionary Force (BEF), 1915

Which of the following novel aspects of World War I contributed to the action described in the passage?

The Allies’ ability to attack German forces with military aircraft
The capability of British tanks to repel machine-gun fire
The attempt to block supply shipments in the Atlantic by using submarines
The stalemate and high casualties caused by trench warfare on the western front