题目内容：
根据下列材料，回答题：Flow control is a function that prevents network congestion by ensuring that （ 1 ）do not overwhelm（ 2 ）>with data．There are three commonly used methods for handling network congestion .（ 3 ）is used by network devices to temporarily store bursts of excess data in memory until they can be processed．（ 4 ）are used by receiving devices to help prevent their buffers from overflowing .（ 5 ）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．
请选择（ 1 ）处最佳答案：
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答案解析：