Once the powder keg was ignited, what made it difficult to stop the chain of events that led to all-out war in europe in 1914? question 5 options:
a. nations responded to threats to their allies by mobilizing their militaries.
b. the policy of isolationism followed by european nations had been largely ignored by 1914.
c. european leaders believed a war in europe would revive their struggling economies.
d. a quick, reliable system of communication was not available to foreign ministers.

A. Nations responded to threats to their allies by mobilizing their militaries.

Explanation:

The outbreak of World War I was greatly due to the system of alliances made between the powerful European countries of the time.  This system obligated a country to go to war if its ally was being threatened or attacked.  

There were 2 main alliances on the eve of WWI, the Triple Alliance between Germany, Austria-Hungary, and Italy, and the Triple Entente between France, Britain, and Russia.

Once the "powder keg was ignited" all of these countries began mobilizing their armies in order to support and uphold their alliances.

there is no photo, therefore i can not answer your question.