Describe the locus L shown in the diagram below

A.
Locus of points equidistant from X and Y 
B.
Locus of points equidistant from X and Z 
C.
Locus of points equidistant from (bar{ZX}) and (bar{ZY}) 
D.
Locus of points equidistant from (bar{XY}) and (bar{ZY})