葡萄胎清官术后出现哪种情况可不考虑为侵蚀性葡萄胎( )

A．葡萄胎吸宫术后100天，β-HCG仍持续阳性

B．葡萄胎吸宫术后β-HCG曾一度下降到正常水平，后又迅速上升到异常水平

C．葡萄胎清宫术后5个月，出现肺、脑转移灶， * * 出现紫色转移性结节

D．葡萄胎清宫术后4个月， * * 出现紫色转移性结节

E．葡萄胎清宫术后1年出现咳嗽，胸片出现转移灶

Both bus and tree topologies are characterized by the use of multipoint (16) ．For the bus，all stations attach，through appropriate hardware (17) known as a tap，directly to a linear transmission medium，or bus．Full-duplex operation between the station and the tap allows data to be transmitted onto the bus and received from the (18) ．A transmission from any station propagates the length of the medium in both directions and can be received by all other (19) ．At each end of the bus is a (20) ，which absorbs any signal，removing it from the bus．

A．routers

B．stations

C．servers

D．switches