题目

计算 （1） （2） 答案：解：原式=3-1 =2； 解：原式=22+42-2 =2+4-12 =52.The World Health Organization warned that Asian countries __________ attentive to bird flu since Asia ___________ got rid of the disease completely.A．should keep; hasB．must remain; has notC．ought to stay; has beenD．shall be; has not been