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