Flow control is a function that prevents network congestion by ensuring that (66) do not over-whelm (67) with data. There are three commonly used methods for handling network congestion. (68) is used by network devices to temporarily store bursts of excess data in memory until they can be processed. (69) are used by receiving devices to help prevent their buffers from overflowing. (70) is a flow-control scheme in which the source device requires an acknowledgment from the destination after a certain number of packets have been transmitted.

A．Buffer

B．Source-quench messages

C．window

D．Windowing

E．Buffering

老年人的代谢和排泄的特点（）。

A.代谢和排泄都加快

B.代谢和排泄都减慢

C.代谢加快，排泄减慢

D.代谢和排泄均有时快、有时慢

E.代谢减慢，排泄加快