A. Cows that have give birth to calves. B. Cows that have produced milk. C. Cows that are less than 30 months old. D. Cows that cannot stand up. 参考答案:D 答案解析:[定位] 根据题干中的constitutes high percentage,可以定位到第一段第二句。 [解析] 根据第一段第三可知美国农业部估计每年有十三万到十九万五千只downers被屠宰,
第11题: [单项选择]核医学最基本的显像仪器() A. γ照相机 B. SPECT C. PET D. 甲状腺功能测定仪 E.活度计 参考答案:A