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 (1) to the IP layer. A TCP (2) Accepts user date streams from local process, breaks them into pieces not exceeding 64KB, and sends each piece as a separate IP (3) .When datagrams containing TCP date 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 (4) them as need be. Datagrams do arrive may well do so in the wrong order, it is also up to TCP to (5) them into messages in the proper sequence.
A．reassemble
B．reduce
C．re-create
D．retransmit
参考答案：A
解析：[参考译文] 每一种支持TCP的机器都有一个TCP传输实体，或一个库过程，或一个用户进程，或者是一个内核的一部分。在每一种情况下，它都管理着TCP流和通向IP层的接口。TCP实体从本地进程接收用户数据流，然后把它们划分成长度不超过64KB的段，并把每一段作为一个独立的IP数据报进行发送。当包含TCP数据的数据包到达机器时，它们会被交给TCP实体，重新构造成原来的数据流。
IP层不能保证数据报正确地传输，所以在必要时必须由上层的TCP采用超时重传机制。数据报可能会不按顺序到达，也需要由TCP把它们按正确的顺序进行重组。