1-b; 2-b; 3-c; 4-a; 5-c; 6-b; 7-b; 8-d; 9-a; 10-b; 11-b; 12-a; 13-a; 14-c; 15-d; 16-c; 17-a; 18-d; 19-b; 20-d; 21-b.