Answer:

Explanation:
Given data

To find
Magnitude of the net magnetic field B
Solution
The magnitude of the net magnetic field can be find as:

The temperature of 20°C is equal to 68.0<span>°F</span>
Your answer is A, Ocean Waves- because A mechanical wave is a wave that is an oscillation of matter, and therefore transfers energy through a medium. Ocean waves do just that :)
Hope this helps!!