21. In face of _______ failure , it is the most important to keep up__________good state of mood .
A. /;
a B.
a; /
C.
the; /
D. /;
the22.
Most animals have little connection with animals of a different kind , _______
they hunt them for food .
A.
if B while C.
unless D.
as23.____
Sunday,
the students are at home.
A.
Being B.
To be C.
It is D.
It being