We know a computer is a machine that processes data (stored in main memory) into information, under control of a stored program. We also know that, internally, a computer is a binary machine; thus the data and the program instruictions must be stored in binary form. Characters are represented in (71) . Numbers are stored as binary numbers, with each bit’s positional value significant. A computer’s main memory is divided into bytes, words or both (depending on the system), and each of these basic storage units is assigned an (72) . Using this address, the processor can read or write selected bytes or words.

The processor consists of a clock, an instruction control unit, an arithmetic and logic unit, and registers. Once a program is stored in main memory, the processor can begin to execute it. During (73) , the instruction control unit fetches an instruction from main memory; during (74) , the arithmetic and logic unit executes it. Precisely timed electronic pulses generated by the clock drive this basic (75)

（75）处填（）。

A．clock pulse

B．instruction

C．memory access

D．machine cycle

哪类媒体的出现，引起了教育的一次重大变革（）

A.语言

B.文字和纸

C.印刷术

D.电子媒体