下列对PLC输入继电器的描述正确的是( )。
A. 其线圈只能由外部信号来驱动
B. 其线圈只能由程序来驱动
C. 输入继电器的线圈既可以由外部信号来驱动又可以由程序来驱动
D. 以上说法都不对
The author of this essay was an English tourist.
A. 对
B. 错
The idea of linking the British Isles with Europe started in the early 20th century.
A. 对
B. 错
The Chunnel will facilitate the transport between Great Britain and other European countries.
A. 对
B. 错