问题补充：
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
答案：
A. should keep; has
(答案→)B. must remain; has not
C. ought to stay; has been
D. shall be; has not been
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