排序图

设等差数列{a_n}的前n项和为S_n，若2a₈=6+a₁₁，则S₉的值等于[ ]

 A．54

B．45

C．36

D．27

下列各组物质中，等物质的量的两种有机物充分燃烧，消耗氧气的量相同是

A．C₃H₄和C₂H₆

B．C₃H₆和C₄H₈O

C．C₃H₆O₂和C₃H₈O

D．C₃H₈O和C₄H₆O₂

大跨度桥梁可以选用的结构形式是（）。

A.砌体结构

B.排架结构

C.筒体结构

D.拱结构

TCP functions at the Open System Interconnection (OSI) (61) layer, or Layer 4. Its chief responsibility is to ensure (62) end-to-end connectivity. IP, located one layer down, at the OSI network layer, or Layer 3, communicates the addresses of each (63) sender and receiver to the routers along the way. Routers and Layer 3 switches can read IP and other Layer 3 (64) . This information, combined with routing tables and other network intelligence, is all it takes to get (65) the room or around the world via TCP/IP.

（63）是（）

A.packet

B.packets

C.packet’s

D.packets’