Which of the Following Statements Is True

Multiple Choice

Which of the following statements is true?

A) When two harmonic waves of the same frequency and wavelength but differing in phase combine,the resultant wave is a harmonic wave whose amplitude depends on the phase difference.
B) A phase difference between two waves can be the result of a difference in path length.
C) A path difference of one wavelength is equivalent to no phase difference at all.
D) A phase difference between two waves can be the result of reflection from a boundary surface.
E) All of these are correct.