医患关系的特点是（）
A.以医疗活动为中心，以维护健康为目的
B.是帮助性的人际关系
C.以患者为中心
D.以上均是
参考答案：D
A．小球振动的周期为2s
B．小球速度变化的周期为4s
C．小球动能变化的周期为2s
D．小球重力势能变化的周期为4s
when the dispute over duty payment arises between the duty payer and the Customs, the duty payer should first pay the duty and then, within ______ days of the issuance of the duty memo, apply to the Customs in writing for a reconsidertation of the case.
A．10 daysB．20 daysC．30 daysD．50 days
