问题：
The computer is very useful in our life, ________it? .
[ ]
A. isn"t
B. wasn"t
C. hasn"t
D. doesn"t
The computer is very useful in our life, ________it? .
B. wasn"t
C. hasn"t
D. doesn"t
[ ]
A. isn"t B. wasn"t
C. hasn"t
D. doesn"t
参考答案：