Gorbachev implemented a ton of radical reforms, which is just one of many things that led to the fall of the Soviet Union. Also, 1991 is the year the Cold War ended.
One observation definitely disproved the Ptolemaic<span> model, although it didn't prove that Copernicus was right. This was the observation that Venus has phases, much like our Moon does.</span>
Answer:
C. Hideki Tojo
Explanation:
In November and December of 1943, U.S. President Franklin D. Roosevelt met with Chinese President Chiang Kai-shek and British Prime Minister Winston Churchill in Cairo, Egypt, to discuss the progress of the war against Japan and the future of Asia.
This would be the definition of an obligation.