物联网中（）对接入层进行数据分组传输的汇聚、转发与交换。
A.行业应用层
B.汇聚层
C.应用层
D.管理服务层
参考答案：B
I don’t understand how you got a ticket. I always _____ you _____ a careful driver.
A．think;are
B．am thinking, are
C．thought, were
D．think, were
再生性钠泵
