Each machine supporting TCP has a TCP transport entity, either a library procedure, a user process, or part of the kernel. In all case, it manages TCP streams and（）to the IP layer. A TCP（）accepts user data streams from local process, breaks them into pieces not exceeding 64KB, and sends each piece as a separate IP（）. When datagrams containing TCP data arrive at a machine, they are given to the TCP entity, which reconstructs the original byte streams.

The IP layer gives no guarantee that datagrams will be delivered properly, so it is up to TCP to time out and（）them as need be. Datagmms do arrive may well do so in the wrong order, it is also up to TCP to（）them into messages in the proper sequence.

A TCP（）accepts user data streams from local process.

A．connection

B．file

C．entity

D．destination

一位患有囊性纤维化的11岁男孩，因金黄色葡萄球菌反复感染肺部，出现喘息、咳痰、发热、呼吸急促和体重减轻而入院。检查发现患者支气管扩张，肺膨胀不全并伴肺部纤维化，细菌培养发现在肺部有革兰阴性杆菌，该菌氧化酶阳性，有动力，能产生带萤光的水溶性色素。

该病原菌产生的具有抗吞噬作用的物质是（）

A.脂多糖

B.鞭毛

C.藻酸盐

D.弹性蛋白

E.毒素A