A．work the same number of hours; same education, age and union status; live in different regions of the country.
B．live in the same region of the country; same age and union status; work same num her of hours.
C．worked for the government; lived in the same region of the country; education; same age; union status and education.
D．work the same number of hours; same age, union status and education; lived in the same region of the country.