<span>Sound waves with frequency higher that 20,000 Hz are referred to as "Ultrasonic"
Hope this helps!</span>
The answer is A. Bob (<span>object's length)
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If both particles have the SAME electrical charge, then they repel.
If they have DIFFERENT electrical charge, then they attract.
Protons have + charge .
Electrons have - charge .
So two protons (A) or two electrons (D) push apart.
One proton and one electron (C) pull together.
