General Science
Kilohertz is a unit which measures

Electric resistance
Power used by a current of one ampere
Voltage
Electromagnetic radio wave frequencies

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General Science
The dark lines in the solar spectrum are due to

Absorption of corresponding wavelengths by the prism used in the photograph.
Absence of corresponding wavelengths from the light emitted by the core of the sun.
Absorption of corresponding wavelengths by the outer layers of the sun.
Destructive interference between waves of certain definite wavelengths.

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