Students learning English find the news a useful______of language practice. To improve their listening comprehension, they listen to the news on the radio and watch it on television.

A．resource

B．origin

C．source

D．illustration

常见的电网中的主要安全自动装置有哪些（）

A.低频、低压解列装置

B.振荡（失步）解列装置

C.切负荷装置

D.自动低频、低压减负荷装置

E.备用电源自投装置