第19题: [单项选择]It is one thing to locate oil, but it is quite another to ______ and transport it to the industrial centers. A. permeate B. extract C. distinguish D. concentrate 参考答案:B 答案解析:extract意为“取出,抽出;提取,提炼”,例如:Scientists can extract precious medicines from ordinary substances .科学家能从普
第20题: [单项选择]下面哪种疾病可造成视力减退和失明 A. 结膜炎 B. 重症沙眼 C. 高度近视 D. 弱视 E. 泪囊炎 参考答案:B