Could world war 2 have been prevented?

Ineed answers 5 and 6 on my social studies homework reply to this question i posted

After world war ii, the world discovered that nazi germany had murdered millions of innocent people as part of the holocaust. seeing that human beings could treat one another so horribly changed the way many people looked at war, government, and minority rights. how could these changes have impacted the study of history?

Pl asap what explorer first discovered a water route from europe to india? a. john cabot b. vasco da gama c. bartholomew diaz d. ferdinand magellan