Answer:
B. An electric current into a magnetic field
Explanation:
The generation of electrical power requires relative motion between a magnetic field and a conductor. In a generator, mechanical energy is converted into electrical energy. The electricity produced by most generators is in the form of alternating current.
Amagat's law of additive volumes states that we can simply add up the individual volumes of each gas (provided they are at the same temperature and pressure) to get the total volume of the mixture. Conservation of volume is an acceptable assumption for gases (but not always for liquid mixtures). This works for gases since the molecules are very small and only take up a minimal amount of space in a gas.
The energy used to plunk guitar strings to make sound is mechanical energy which gets converted to kinetic energy and finally to sound energy which produce the sound.