Answer
Choice C.
Work Step by Step
Students who originally heard a loud tone were at a point of constructive interference, where a crest from one speaker met a crest from the other speaker. Now these students hear nothing, so at their point a crest now meets a trough. The phase relationship between the waves has been changed. This is choice C.
We note that points of destructive interference were also changed to points of constructive interference, as expected.
