何谓展频（Spread Spectrum）？

1、The immigrants spread unevenly across

The immigrants spread unevenly across the country,with（）having the largest percentage of immigrants.ANortheastBthe WestCMidwestDthe South

2、Radiation can spread a fire by （）.

Radiation can spread a fire by （）.Atransmitting the heat of a fire through the ship s metalBburning liquids flowing into another spaceCheated gases flowing through ventilation systemsDthe transfer of heat across an unobstructed space

3、毒效应谱（spectrum of toxic effects）

毒效应谱（spectrum of toxic effects）

4、涂布平板法（spread plate method）

涂布平板法（spread plate method）

5、Fire dampers prevent the spread of fir

Fire dampers prevent the spread of fire by（）.AconvectionBconductionCradiationDdirect contact

6、何谓跳频（Frequency-Hopping Spread Spectrum

何谓跳频（Frequency-Hopping Spread Spectrum）？