Why is travel through Central America difficult?

There are a lot of crimes at night there.

Explanation:

Central America is quite safe for solo travelers. As long as you avoid isolated areas and don't travel alone at night, you'll be able to avoid the most common issues tourists face, such as petty crime.

d. i assume the underlined word is "role." reformat if it isn't.

explanation:

role is closest to part because when replacing words, "playing a vital decision," "playing a vital activity," and "playing a vital dollar" don't make logical sense. the only meaningful choice is "playing a vital part."

this fits one of merriam-webster's definitions of role: "a function or part performed especially in a particular operation or process."