What brought an end to the system of self labor system

Which of the following is one example of an ideological conflict that became one of the causes of world war ii?

Which of the following world and national events led to a new view of people with disabilities in the us:     a.  world war i and ii veterans with disabilities returned home after the wars.b.  john f. kennedy was elected president and had a sister with a disability.c.  the civil rights and feminist movements.d.  all of the above.

What mountains did the first transcontinental railroad cross