21. In face of _______ failure , it is the most  important  to keep up__________good state of mood .
¡¡¡¡A. /; a      B. a; /           C. the; /           D. /; the
¡¡¡¡22. Most animals have  little connection with animals of a different kind ,  _______ they hunt them for food .
¡¡¡¡A. if         B while            C. unless            D. as