简述无线信号传播损耗的定义?
参考答案:
传播损耗是指对于某一无线电链路,从发射天线输出端的信号经过一定的传播路径,到达接收天线的输入端时,功率电平的损耗值.
冬天,一直被冰冻着的衣服也会变干,这说明冰由________态直接变为________态了.
The old lady didn't know _____ when the house caught fire. [ ]
A. how to do
B. how to do it
C. what to do
D. what to do it