i.e |z - 0| = |z -(1+i)|
It means the distances of (all) z from the points O(0,0) and from A(1,1) are equal. So the equation defines the locus of a point which is equidistant from these 2 given points O & A, viz. the perpendicular bisector of the line segment OA. Draw this perpendicular bisector and the dotted line thru the Origin O and parallel to this bisector. Take any point B on the bisector. You'll find Arg(z), angle XOB, satisfies D). The line OB never crosses the dotted line.