Countries with a low standard of living usually have ___ than countries with a high standard of living.

Lower GDP per capita.

Explanation:

GDP per capita represent the amount of average economic output that one person has in a certain country. Higher GDP per capita means that the each person has more disposable income that they can spend to purchase various types of goods or services.

As a person's purchasing power increase, that person will become more likely to be able to afford tertiary products outside their basic needs (For example, after purchasing their foods, clothes, and shelters they might still have money left-over to purchase jewelries or nice cars) . This is why lower GDP per capita tend to resulted in lower standard of living.

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."