Spread spectrum simply means that data is sent in small pieces Over a number of the (46) frequencies available for use at any time in the specified range. Devices using (47) spread spectrum (DSSS) communicate by (48) each byte of data into several parts and sending them concurrently on different (49) . DSSS uses a lot of the available (50) , about 22 megahertz (MHz) .

A．splitting

B．combining

C．packing

D．compacting

计算题：调查黄瓜霜霉病田间发病情况数据如下，请计算其发病率及病情指数。