第20题: [单项选择]牙源性腺样瘤的好发部位为() A. 上颌切牙区 B. 下颌切牙区 C. 上颌单尖牙区 D. 下颌单尖牙区 E. 磨牙区 参考答案:C
第21题: [填空题]Not until the ______ were the cars that could burn natural gas invented. 参考答案:1930s 答案解析:[解析] 题干涉及到使用天然气作为燃料的汽车的发明,在natural gas basics的最后一句提到But cars that could burn natural gas didn’t appe