单项选择题 ASCII is a 7-bit code used to represent numeric, alphabetic, and special printable characters. It also includes codes for control characters, which are （）.

单项选择题 In most wide area networks, the communication subnet consists of two distinct components：transmission lines and （）.

单项选择题 在下列各种类型的I/O技术中，对CPU依赖最小的是（）。