单项选择题

A．From the starting point back to the earth.
B．Several hundred kilometers.
C．A certain height.
D．About 50 kilometers.
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单项选择题
A．Teach half days.B．Take a longer tour.C．Tour the country.D．Rest for the day.
A．Teach half days.
B．Take a longer tour.
C．Tour the country.
D．Rest for the day.
单项选择题
A．Microwaves are strange electric waves.B．Microwaves travel in straight lines and do not follow the curve of the earth’s surface.C．There are not any wires to send microwaves.D．We must amplify microwaves in relay stations.
A．Microwaves are strange electric waves.
B．Microwaves travel in straight lines and do not follow the curve of the earth’s surface.
C．There are not any wires to send microwaves.
D．We must amplify microwaves in relay stations.
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