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.

it is also up to TCP to（）them into messages in the proper sequence.

A．reassemble

B．reduce

C．re-create

D．retransmit

前列腺分泌部的上皮为（ ）

A．单层立方上皮

B．单层柱状上皮

C．假复层柱状上皮

D．单层立方、单层柱状和假复层柱状均可见