Two coherent sources, A and B, emit light waves in a medium. The light waves superpose to produce an interference pattern. Which of these is true of sources A and B?
A) The two broad sources of light were far apart from each other.
B) The waves emitted by the two sources have different wavelengths.
C) The waves emitted by the two sources have constant phase difference.
D) The two sources of light had to be obtained from two different sources.