医疗物品对人体的危险性是指物品污染后造成危害的程度,根据其危害程度将其分为几类()
A.二类
B.三类
C.四类
D.五类
E.六类
参考答案:B
下列物体在运动过程中机械能守恒的是( )
A.被匀速吊起的货物
B.做自由落体运动的小球
C.在引桥上匀速行驶的汽车
D.自高坡无阻力自由下滑的滑雪运动员
Mr. Jones, this is Sean, an English teacher from the United States.()
A.What can I do for you?
B.Nice to meet you.
C.Please keep in touch.
D.Haven't seen you for ages.