题目内容：
根据下列题干，回答题：In the following essay，each blank has four choices．Choose the best answer and write down on the answer sheet．
Spread spectrum simply means that data is sent in （ 1 ）pieces over a number of the discrete frequencies available for use at any time in the specified range．Devices using（ 2 ）spread spectrum(DSSS)communicate by splitting each（ 3 ）of data into several parts and sending them concurrently on different （ 4 ） ,DSSS uses a lot of the available （ 5 ），about 22 megahertz(MHz)．
请选择（1）处最佳答案：
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答案解析：