根据下面的文字资料回答 71～75 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)．
第71题：文中（ 1 ）处正确的答案是（ ）。
A．small
B．high
C．low
D．long
