The answer is C.
After the assassination Austro-Hungary sent an ultimatum to Serbia to investigate the assassination in Serbia, but Serbia declined the ultimatum, so Austro-Hungary declared war to Serbia. Then Russia declared war to Austro-Hungary and Germany declared war to Russia. Then the Ottoman Empire joined Germany and Austro-Hungary and they created an alliance and some other countries joined as well. After that, Great Britain, Russia and France created an alliance as well, and some other countries also joined their alliance. That's a short summary of how the WW1 started.
D. The growing political influence of immigrant groups in the colonies
The U.S. President Trump, after the past few presidents have been holding this off, Has finally made the decision and signed the waiver making the decision to move the U.S. Embassy from Tel Aviv to Jerusalem. Though they already could make this decision long ago, every six months, the past presidents kept holding it off. There is more to it, but the simple answer is Jerusalem. However your question does not seem legit... why do you ask this?
