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 small pieces over a number of the (16) frequencies available for use at any time in the specified range. Devices using (17) spread spectrum(DSSS) communicate by (18) each byte of data into several parts and sending them concurrently on different (19) . DSSS uses a lot of the available (20) , about 22 megahertz(MHz).

A．direct-sequence

B．discrete-sequence

C．duplicate-sequence

D．dedicate-sequence

鸡内金除具有健胃消食功效外，还具有的功效是（）。

A、散瘀行滞

B、涩精止遗

C、降气化痰

D、健脾开胃