The last straw that caused that triggered the outbreak of WWI was the assassination of Archduke of Austria - Hungary Ferdinand and his wife on June 28, 1914 by a Serbian nationalist with ties to the secretive military group known as the Black Hand.
Due to this, one month later, Austria - Hungary declared war on Serbia. The situation was joined by other countries based on which alliance they were in. A group of alliances between major powers in Europe had been formed or were in the process of being formed by this time.
C is the answer for this question
The discovery of metal/ using it to make tools
Answer: Jewish
Explanation: Jesus of Nazareth was a first-century Jewish religious leader. If you need evidence read the sermon on the mount (Matthew 5-7).
Answer: The Soviet Union and the United States stayed far apart during the next three decades of superpower conflict and the nuclear and missile arms race. Beginning in the early 1970s, the Soviet regime proclaimed a policy of détente and sought increased economic cooperation and disarmament negotiations with the West.
Explanation: google