问题
The World Health Organization warned that Asian countries __________ attentive to bird flu since Asia ___________ got rid of the disease completely.
A:should keep; has
B:must remain; has not
C:ought to stay; has been
D:shall be; has not been
B:must remain; has not
C:ought to stay; has been
D:shall be; has not been
正确答案是：
