单项选择题

The highly efficient modern communication system began ______.

A．over a century ago
B．in the middle 1960s
C．in the late 1980s
D．in the year 1980
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单项选择题
Which of the following correctly describes Cosmos I
A．It is a 3-ft. metal pod.
B．It has eight 35-ft. metallic wings.
C．It can fly an altitude above 260 miles.
D．When it flies back to Earth, it will fall into pieces.
单项选择题
What is the energy source of this so-called solar-sail vehicle
A．Sunlight.
B．Nuclear.
C．Wind.
D．Electricity.
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