LTE物理层定义了3种下行参考信号，包括小区专用的参考信号、MBSFN参考信号和（）。
参考答案：终端专用参考信号
The bridge was completely __________after it rained for 14 days and people had to cross the river
by boat. [ ]
A. damaged
B. harmed
C. destroyed
D. injured
对原子吸收分光光度计的光源为什么要进行调制？调制的方法有哪几种？
