A. was discouraged B. was enforced by law C. was prohibited by law D. was introduced 参考答案:B 答案解析:根据第一段第二句话"In the twenty years that the Clean Air Act has mandated unleaded gas use in the United Sta
第13题: [单项选择]马斯洛将人的基本需要分为五个层次,由低到高依次为() A. 生理,爱与归属,安全,尊重,自我实现 B. 生理,安全,爱与归属、尊重,自我实现 C. 安全,生理,爱与归属,尊重,自我实现 D. 安全,生理,尊重,爱与归属,自我实现 E. 生理,安全,尊重,爱与归属,自我实现 参考答案:B