It created a government system with the ideologies of republic, the foundation of what is to come in the U.S. Constitution. It adopted personal freedoms and voting for public of offices.
The Nazi-Soviet pact between the Nazi Germany and the Soviet Union gave Stalin the chance to expand the USSR's territory toward the Eastern Europe. Therefore, the answer is letter D. To add up, the non-aggression pact allowed both superpowers to invade Poland, which is a vital nation for trading hub.