Answer:
B. the center of the circumscribed circle of the triangle.
Given is :
The three locations where Marcia travels represent the vertices of a triangle.
Marcia wants to move to an apartment that is equidistant from these three places. She must find an apartment that is at the circumcenter of the triangle.
The circumcenter of a triangle is a point in the plane, which is equidistant from the three vertices of the triangle.