题目内容

3．（）had surpassed radio for home use and entertainment.

A. Communication
B. Television
C. Video camera
D. Personal computer

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4．Using echoes of radio microwaves, radar can detect（）.

A. a car
B. a ship
C. a plane
D. rain

5．The first electronic computer included 18,000（）and used 200 kilowatts of electrical power.

A. transistors
B. vacuum tubes
C. ICs
D. electronic components

6．A transistor is a semiconductor device used to（）electronic signals.

A. produce
B. amplify
C. reduce
D. switch

7．In most applications, vacuum tubes have been replaced by（）and other semiconductor devices.

A. electron tubes
B. transistors
C. silicon
D. germanium