以RNA为模板，，用反转录酶可同时产生单链和双链的 cDNA，双链 DNA是由自身引物引导合成。但这种自身引物引导的合成效率远低于外加寡核苷酸引物引导的合成。
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铁路箱站内外存放的铁路箱发生破损，除能判明责任者外，责任列（）。
A. 装卸单位
B. 集装箱货运员
C. 存放地单位
D. 卸车站货运
When is a switched network that is running the Spanning Tree Protocol considered to be fully converged?（）
A. when all switches have the same BID as the root switch
B. when all switches have received the MAC address of each neighboring switch
C. when every enabled switch port has been assigned a unique identifier
D. when every operating switch port is in either the blocking or forwarding state
E. when all switches are in either client, server, or transparent mode
烟草制品批发企业的设立和烟草制品生产企业固定资产投资审批的法律依据均是（）
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