D would be the best answer
Thhe answer is your last option "led to decline in racist attitudes towards African American and imigrants"
The American cowboy drew many of his customs from ranchers in Mexico.
Yes, it is because they were there and didn't take it from someone else.
The articles of the Constitution explicitly outline:
B - a bicameral nation legislature.
Article I, Section 1 explains how Congress is split into the Senate and House of Representatives, a form of national bicameral legislature.