Question

At the end of World War I, which nation was all that remained of the Ottoman Empire?

Answer 1

I would say Turkey.

Explanation:

The end of WWI finalized a process of decline of the Ottoman Empire already divided and crumbling.

[Ottoman Troops at Gallipoli]

Although during the war the Ottoman Empire (allied of the Germans) conducted several successful operations (resisting the siege of the ANZAC expeditionary force at Gallipoli) its internal enemies were eroding it from within.
It is interesting to remember the Arab Revolt (military "assisted" by the British officer T. E. Lawrence) that led to the formation of Saudi Arabia.

A personal remark: it is important to remember the fact that to be in line with the horrible slaughter that was unfolding in the trenches on the western front, the Ottoman high command decided to invade Russia...in winter (Battle of Sarikamish, Dec-1914 Jan-1915, loosing more than 80,000 soldiers)!