瑞士心理学家皮亚杰把儿童以认知的发展分为四个阶段，其中具体运算阶段为几岁到几岁?()

A、0~2岁

B、2~7岁

C、7~11岁

D、11岁以后

A Bluetooth device can be either a master or a slave and any of the devices within a ___30___can be the master. There is only one master and there can be up to ___31___ 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 ___32___.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 ___33___ mode before it can become active. Within a network, all ___34___ communications are prohibited.

33（）

A. master

B. standby slave

C. parked slave

D. Active slave