Question

Interference is a condition that occurs when _____.

a) one side of a wave moves at a different speed than the other

b) a wave encounters an obstruction

c) two or more waves overlap and combine

d) the source of the wave’s vibration loses energy

Answer 1

For the answer to the question above, To set up a stable and clear interference pattern, two conditions must be met: The sources of the waves must be coherent, which means they emit identical waves with a constant phase difference. So I think the answer is c.two or more waves overlap and combine.
Because waves needs to be monochromatic or in single wavelength