You are walking around a large open field. The only objects nearby are two identical speakers set some distance apart, which are both producing sound, in unison, with a wavelength of 4 m. As you wander around the field, you notice that at certain locations, the sound you hear is surprisingly loud, while at others it seems unusually quiet. You conclude that you are observing the effects of interference between the two sources of sound waves. For each of the locations given below, indicate what sort of interference would occur at that point.