A Bluetooth device can be either a master or a slave and any of the devices within a (1) can be the master. There is only one master and there can be up to (2) active slave devices at a time within a single network. In addition, a device may be a standby slave or a parked slave. There can be up to (3) parked slaves. If there are already maximum number of active slaves, then a parked slave must wait until one of the active slaves switches to (4) mode before it can become active. Within a network, all (5) communications are prohibited.

3（）

A．127

B．255

C．511

D．1023

脊髓灰质炎的主要传染源是（）

A.无症状病毒携带者

B.猴

C.病人

D.隐性感染者

E.猩猩