D. Copper and Gold
Copper and gold are used a lot in electrical applications.
Air and wood are insulators and glass is also kinda bad...
Metals can form a sea of elections which causes them to be good conductors of energy
The product of (wavelength) times (frequency) is always
the same number ... it's the speed of the wave.
So if the speed of the wave doesn't change, the product
of (wavelength) times (frequency) doesn't change.
That means that if the wavelength OR the frequency changes,
the OTHER one has to change by the same factor in the opposite
direction, in order to keep their product unchanged.
If the frequency in INcreased by a factor of 4,
the wavelength must DEcrease by a factor of 4.
If the frequency becomes 4 times as great as it was,
then the wavelength becomes 1/4 as long as it was.
(Please don't say "4 times shorter". That's meaningless and I hate it.)
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