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. Datagrams 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

下列不能使皮质激素的抗炎作用挺高的结构变化是

A．6α位、9α位引入氟

B．16α位引入羟基

C．16α位引入甲基

D．21位羟基变为醋酸酯

E．1，2位引入双键