I'll first explain what the non-aggression pact was. It was an agreement that the Soviet Union and Germany would take no military action against each other. To answer your question it is B. The pact was to make sure he could safely attack Poland.
7.7 billion people on the earth
C. Bacterium yersinia pestis is the right answer :)
During the Cold War there was a concern in the United States over the expansion of communism. This fear of communism manifested itself in the domino theory an idea which governed much of us foreign policy starting in the 1950s. The domino theory was essentially the idea that if one nation fell to communism its neighboring counties would as well and this process would repeat itself almost resembling a row of dominos falling (hence the name). Because of this theory many political leaders in the us feared that if former French colonies like Vietnam fell to communism than their neighboring counties would as well including Laos, Cambodia, etc.